General consensus is; just take Soldier.
Using it as your 1st class allows you to respec into any other weapon class you like (you can't respec your 1st class, only your 2nd)

And take the Crystal Bombs (or Spellbinder Aura if you plan to use magic)

First off, each class does receive a few things which can only be obtained if selected at the start and are NOT available if selected as your 2nd class when you unlock that (after defeating the Dark Knight) These are:

Wizard: (Casting Tome & Spell Blade)
Wizard's Might: All abilities cost 5 less soul energy to use
Wizard's Mastery: Using a phoenix plume will give 15 soul energy to use for abilities

Soldier: (Longsword & Shield)
Soldier's Might: Blocking attacks gives you soul energy to use for abilities
Soldier's Mastery: Triples soul energy gained from blocking
NOTE: From others and personal experience... Soldier and blocking are the new king. Don't bother parrying, just block and "Perfect Block" and pair that with any weapon you like, tho yes longswords work quite well

Assassin: (Daggers)
Assassin's Might: Dodging attacks grants soul energy to use for abilities
Assassin's Mastery: Soul energy gained by dodging attacks increased by 4

Acolyte: (Scythe)
*Able to restore broken Death Idols (aka grants extra places for you to rest)
Acolyte's Might: Killing enemies grants soul energy to use for abilities
Acolyte's Mastery: Doubles the soul energy gained by killing enemies
NOTE: Acolyte's uniques are nice for killing trash, but a lot less useful on single strong targets... like bosses

Noble: (Halberd & Spear)
*Access to a unique merchant: Braeorn[deathsgambit.wiki.fextralife.com]
Noble's Might: Using items grants soul energy for abilities
Noble's Mastery: Increase essence gained from killing enemies by 15%
The special merchant saves you:
50 shards per Armor Scrap
35 shards per Crystal Bomb
And provides access to:
A Unique +5 Halberd for 1200 shards
Fire Bomb for 250 shards each (~2x the damage for 12.5x the cost of a Crystal Bomb)
Gaian Blood for 250 shards each
Abyssal Eye for 100 shards each

Sentinel: (Greatsword & Greathammer)
Sentinel's Might: Parrying grants soul energy to use for abilities
Sentinel's Mastery: Doubles the soul energy gained by parrying enemies
NOTE: Parrying has become a lot less important with the addition of "Perfect Blocking"

Blood Knight: (Axe)
Blood Knight's Might: Regain Health that was recently lost if you quickly retaliate with an ability
Blood Knight's Mastery: Taking damage gives you soul energy to use for abilities
NOTE: The BK's "Rally" effect is a LOT less powerful than it was before the Afterlife update, but is still unique

Normally we'd just use the wiki[deathsgambit.wiki.fextralife.com] for this part but... it kind of sucks; feel free to improve it if you can get the permission to do so. Atm the talent trees themselves are missing from the wiki so you don't know what is required to unlock what, some data is out of date, and the noble page is missing the whole spear line of talents... so ya let's just post our own here.

All the following talents are read off the talent trees from top left to bottom right, with classes listed in the order the game sorts them on the 2nd class screen (as seen at the bottom of each screenshot)

Wizard:

• Burning enemies hit with fire magic explode, taking extra damage and damaging enemies around them
  
• Hitting burning enemies with fire 2, causes them to explode again
  
• Spell blade finisher makes the orb cast animations much faster. Lasts 10 seconds
  
• Creating a tome orb reduces all other ability cooldowns by 2 seconds
  
• Animation for casting lightning 1 is faster and strikes one additional time
  
• Using lightning 2 infuses you with lightning. All lightning damage increased by 20% for 20 seconds
  
• Casting lightning and fire orbs together, now creates 3 orbs at a time
  
• Animation for dark orb 1 ability is faster
  
• If dark 2 kills an enemy, the attack repeats itself
  
• Casting Dark and Fire orb now creates a mine that explodes 3 times

Soldier:

• Perfect blocking reduces all ability cooldowns by 8 seconds
  
• Recover from being shield-broken 50% faster
  
• Whenever you heal, you leave behind a small area that heals you overtime. Heals 5% every second for 10 seconds
  
• Fortitude ability now makes you completely invincible, and lasts 4 seconds. Its cooldown is increased by 15 seconds
  
• All shields block as if they are S ranked, reducing stamina lost from block attacks
  
• Hitting a bleeding enemy with Winding Hew resets the bleed timer and makes it deal 20% more damage over time
  
• Heroic Lunge deals double damage if you are under 25% health
  
• Dealing damage to bleeding enemies with a longsword roll attack lowers all ability cooldowns by 10 seconds
  
• Lightning strikes at the end of Storm Caller's sword, dealing extra damage
  
• Bows now scale with strength instead of finesse
  
• All lightning damage taken reduced by 10%
  
• All fire damage taken reduced by 10%
  
• If soul crash were to blind an enemy, it reduces ability cooldowns by 10 sec

Assassin:

• Getting shield broken lowers all ability cooldowns by 10 seconds
  
• Blink increases all damage dealt by 4%. Effect lasts until 2.5 seconds pass without hitting an enemy
  
• Hitting a bleeding enemy with a dagger roll attack adds 3 seconds to the bleed timer
  
• Dealing a killing blow to an enemy with a bleed effect will cause it to explode into a cloud of blood that deal damage to enemies in it
  
• Using assassinate creates a shadow copy of yourself that deals damage where you used the ability. Lasts 4 seconds
  
• Dagger combo finisher deals double damage if under 20% health
  
• Reduces Gouge cooldown by 15 seconds
  
• Your next dagger roll attack after using gouge also blinds enemies
  
• Ability. You become invisible to non-boss enemies. 60 soul energy cost. 50 second cool down
  
• Healing leaves behind a small area that doubles ability cooldown speeds while standing in the area. Lasts 10 seconds
  
• Dodge rolling reduces all ability cooldowns by 1 second

Acolyte:

• Being shield broken gives 20 soul energy
  
• Hitting an enemy with Crash Down increases soul energy gained from attacks by 3 for 12 seconds
  
• Scythe attacks deal 4% more damage when over 90 soul energy
  
• Max Soul Energy increased by 40
  
• Reap ability animation is faster and the buff lasts 5 more seconds
  
• Scythe combo finisher deals double damage if under 20% health
  
• If you have over four stacks of reap, your main scythe combo is much faster. When this effect is active, reap timer cannot be reset
  
• Ability. You cannot go below 1 health for 8 seconds
  
• All dark damage taken reduced by 10%
  
• Abilities cost 5 more soul energy. All damage increased by 5%

Noble:

• Every 150 soul energy gained by attack enemies, restores 1 bear trap to use
  
• Halberds now scale with Finesse
  
• Longswords now scale with Finesse
  
• Gain 50% more essence whenever you kill an enemy while under 25% health
  
• Negative debuff lasts 25% less time
  
• You now drop crystal bombs behind you as you use the halberd Lunge ability
  
• Picking up items heals you for 5% of your health and increases your soul energy by 20
  
• Perfect blocking makes your next lunge or spear rush deal 50% more damage. Effect lasts 12 seconds
  
• Cyclone ability animation is faster
  
• Halberd combo finisher deals double damage if under 20% health
  
• Ability. Throw a blind trap. Enemies who step on it are unable to attack for 5 seconds
  
• All lightning damage dealt increased by 4%
  
• Spears now scale with strength
  
• Whenever spear rush is used, the next spear rush ability can be used right away and it costs no soul energy
  
• Spear combo finisher deals double damage if all under 20% health

Sentinel:

• All fire damage dealt increased by 4%
  
• Hitting an enemy that is already bleeding with rupture causes them to take 20% more bleed damage over time
  
• Hitting a bleeding enemy with a greatsword roll attack adds 3 seconds to the bleed timer
  
• Greastsword combo finisher deals double damage if under 20% health
  
• X slash curved projectiles come back towards you and deal damage again
  
• Perfect block makes your next roll attack hit grant 25 more soul energy than usual
  
• Upon healing, you leave behind a small area that regenerates your stamina very quickly. Lasts 10 seconds
  
• Attacking with Crash Down increases all damage done by 3%. Effect lasts 24 seconds
  
• Whenever a crash down would blind enemies hit, it also creates an explosion dealing 7x more damage than a regular crashdown
  
• All dark damage dealt increased by 4%
  
• Crushing Tide and Seismic Nova buffs last 10 seconds longer
  
• The explosion for Seismic Nova is now huge
  
• If you have over four stack of Crushing Tide or Seismic Nova, then your main greathammer combo is much faster. When this effect is active, the timer of this effect cannot be reset

Blood Knight:

• Ability. Sacrifice 17% of your health for 35 soul energy
  
• Using Unholy Trasfer also reduces ability cooldowns by 7 seconds
  
• Hitting a burning enemy with Flame Blitz, causes them to explode, dealing damage around them
  
• Flame Blitz animation is much faster
  
• Taking damage makes abilities cost 20 soul energy less for 2.5 seconds
  
• Using Unyielding Strike while over 60 soul energy causes enemies hit to bleed and take damage over 16 seconds
  
• Cleaving Throw animation is faster
  
• Deal double damage if you hit a burning enemy with a roll attack
  
• Perfect block retaliation heals you by 4% of your maximum health
  
• Kill an enemy reduces incoming damage by 30% for 5 seconds
  
• Perfect blocking reduces the time of negative status ailments by 5 seconds
  
• Dropping under 10% health activate a buff that lets you heal whenever you deal any damage. Effect lasts 15 seconds and cannot happen more than once every 5 minutes
  
• Abilities cost 5% health but also cost 5 soul energy less

Vados Spear: A decent alternative starting weapon, but you'll also find plenty of them as drops and placed items.

Blindfold: Looks good until you realize it literally blinds you aka try playing the game with your monitor turned off... no thanks

Crystal Bomb x8: These will let you easily kill the 1st Drake Knight elite and thus pick up the [Surging Soul] aura before even seeing the 1st boss... thus they are your best pick here unless you just want all Auras

Gaian Blood x5: A consumable to gain temporary Soul Energy used to power your abilities... you'll find tons, I don't use them and can't even vendor them

Spellbinder's Aura: Drops from Aldwynn Priests (credit: FakeKraid)

Vados Helm: I haven't been able to find this item anywhere else, but there will be better options later on

Shield of Warding: Show up as a placed item early on

Soul Stone x5: You'll end up with tons of these once you unlock the disenchanter NPC, still might help you level up a tad faster

Lenny's Broken Sword: Just a bad weapon with seemingly no up-side

Here is a guide on where / how to use the Crystal Bombs:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1480081483

If I missed anything or got anything wrong feel free to "correct" me in the comments ;-P

Just as a bonus for those who made it this far, here's a secret for you:
After defeating Ione for the 1st time (a non-optional mini boss) a new NPC will spawn in the tutorial area. His name is Fink, a merchant, who many players accidentally kill; either from chasing the crystal lizard near him or not knowing what I'm about to tell you, and thus locking out TWO "questlines" for the rest of their playthrough. You HAVE to buy something from him each time you encounter him, elsewise he'll turn permanently hostile. Each time you encounter him in a new location (as long as he is not hostile) he'll offer better and better items - this is the 1st "questline." Next, you'll want to buy that [Corpse Shield] he is selling, it is not available anywhere else. Once you get to the safe hub area with the NPCs, equip it and show it to Sigur (the knight NPC) by blocking with it in front of her (you might want to exhaust dialogue with her to get a free plume first) Thus begins the 2nd questline... PS anyone know if you can save her?

Other secrets I've stumbled across:
Kill Bast, otherwise he'll start killing your other NPCs. Just don't do it right away, you have time; you'll want to learn his dagger abilities first, and if you talk to him after returning a certain number of other NPCs to the hub he'll also give you a free [Gaian Blood]. Additionally, he has a chance to drop [Dark Leather Boots +3] when killed.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1479377209
This guide details another secret, it just fails to mention that you really do have to wait those 10 minutes and not leave the screen or else you might miss the little guy's return and thus not get the [Immortalite].

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1491261909

Might add more later.