One of two upgrades that change gameplay aside information provided, and a very potent one without doubt. During a mission, time is the most important resource - by cutting precious second from time-cost of activating sentries or downloading cores, you leave less time for beasts to multiply in numbers, to break door blockades, to deplete sentry ammo, to find their ways to flank you (and maybe get a drop on a scientist you're escorting, assuming you didn't rush his rescue before interacting with any cores)... you can just rush with lightning speed before having chances to be defeated.

It loses to A tier upgrades in exactly one situation, and that is when your map next to no cores yet a lot of fighting and flankees. Normally, this shouldn't be the case if you increase your difficulty correctly - by having just download speed and maybe datacore pathfinder, you will be able to get other useful upgrades before you would ever need them.

I think no one who had even few hours of gameplay would disagree that the motion tracker is extremely powerful. You can do without upgrading it at all, winning just by quickly learning the map, but it would be quite difficult a feat, especially at harder difficulty (I'm talking about actual difficulty dictated by breach positions, ability to cut their danger etc, not just beast spawnrate).

First level, directional tracker, already protects you well from being killed from behind assuming you can react. This is also the most useful of four levels, near irreplaceable.
Short range lets you also pinpoint exact numbers of enemies, seeing where it is a horde and where is a lone astro creep.
Long range lets you spot hostiles from afar - which quite good if you don't know the map but want to seal the breach, since there is no "breach pathfinder". Secure the area before too much beasts spawn to handle. Less useful when map is known (such as CotW before random breaches turn on) but still may protect from flankees during scientist escort.
Scientist tracker lets you immediately see them civs and rush there before map gets dangerous. Never bad to have, altro finding "security room" with the map can make it a bit redundant.

This is the second best upgrade, and only loses to download speed due to the fact latter lets you just rush all the datacores from the start (which also may give direction tracker as a bonus) before you would even need the tracker. Also, motion tracker is near-useless against lurking beasts (remedied by using infra vision, however). Of course, ideally you get both maxed tracker and dl speed later on.

Marking every (moving) enemy in range for you to hit improves your ability to hit them substantially. Since marker disappears instantly once enemy dies, you move your weapon faster to shoot the next one.
However, what's better is that icons are fully visible regardless of your battery power - and aim assist's target icons are no exception. You have full target visibility even if you are in otherwise total darkness. Additionally, having your infravision and light systems broken does not affect it, so it's extra redundancy for cases of electronics damage.
Later on, number of enemies would warrant use of more firepower than you can aim with (hello ultra shotgun), and your infravision and battery in general will be strong enough. Still, keeps it neat and well visible, improving your experience.

First level of Infravision is extremely helpful. You get something to rely on at low lights (and at some extent at long ranges where your lights simply don't reach), and you get the one tool to more or less reliably see a still ("lurker") beast. This is so helpful, I can't believe nornware decided to remove additional battery drain upon infravision usage - because there should be disadvantage to using it.

Later levels improve image notably, but don't add new functionality. This is partly QoL at that point, altro it can be convenient enough to use more or less permanently from 50-75% depending on a player.

The second of two upgrades that affect core gameplay and not just information you have, ammo capacity is... not super useful in many cases. Assuming you don't waste too much ammo, you should be doing overall well with what reserves you have, at least until you find an armory to restock. This is especially prominent in easier missions, where map control is abundant and fighting is not.

Still, having better capacity can give you more freedom on when to have to seek armory or spend time at one. And in situations where you have to fight lots of aliens before you even have chance to restock it can mean difference between cutting through horde or running out of ammo and dying.

Generally speaking, having some charge in your battery is better than having it empty. That being said, it's not that important. Ways of recharging are plentiful enough to seldom have to worry about it for the most part. Still, sometimes it comes in handy.

It's important to notice that usefulness of this upgrade would be higher if having empty battery actually meant a lot. But in easier games you should secure area well enough (plus not interrupt your core interaction process with too much fighting, so you refill battery often anyway), and by harder games hopefully you get upgrades. Not battery capacity, I mean. Ones that let you see enemies despite your flashlight nearly ceasing to exist. Infravision, aim assist, motion tracker all help a lot. (You will probably get some battery capacity by then anyway but that's not the point.)

Upgrading your map lets you navigate easier, and gives rough idea of where you weren't yet at. And that's it. You may spot unactivated core nearby after upgrading, but usually if you have some awareness you will spot it anyway. Main use of the map is QoL.
This is especially true for later levels. Especially the last one that would be so good if not the fact you can't actually see your fully revealed map except by going to that area yourself. Seeing some stuff through walls or doors is the only use here and it doesn't actually give you much.

Apply all the same reasoning as with battery capacity. Except that this one doesn't actually give you more capacity, also it's recharge rate is made somewhat redundant by datacores giving you 30/60s of charge for free.
First level is good to have so that you don't spend eternity recharging, after that it's not really helpful, at least until you get to 2s download time.

The trait all pathfinders share is being useful when you actually need the location they're pointing at, and doing nothing in (almost) all other cases. So usefulness of individual pathfinder depends on their target location.
Other trait is that path they select can be suboptimal. They can easily lead you through near breach location sealed by fences, whereas otherwise you would take a route around.
And of course, they are much weaker if the map is well known. In single player especially, as you can make screenshot of the map, then at any moment pause the game and look at it.

Datacore: the best one, I'd give it A-. Reason is that, you always want to know how to reach the next datacore. This really saves time on your datacore hunt - a trait shared with download speed. Route only leads you to the closest datacore, however, and greedily hunting only the closest ones can be weaker in the long run (suboptimal route of getting all cores); still, very helpful in faster+safer mission completion.

Airlock: depends on your memory, but in general B tier. Scientist delivery is made much easier with this (as long as you don't go through danger zone anyway). Escaping reactor meltdown faster may also be of use.

Reactor: B- tier. Saves time a little during a mission, similar to datacore pathfinder - but only once per mission and assuming no cores spawned near reactor (revealing it anyway). Afterwards, you know where reactor is so it's again the matter of memory.

Armory: C tier. You don't often need ammo, but when you do, this can be a lifesaver.

Sentry gun: D+ tier. Sentries only cover certain area, so if you need to cover some area you only want to search for sentries in a nearby vicinity. This tracker at best makes it slightly more comfortable. Maybe you could run from the horde and use the tracker to find a sentry to repel it...? You are likely to not have time to activate the sentry in that case, though, and it can be easier to just shoot them all.

Repair: D tier. Ideally, you don't often need repairs, but when you do... you may actually lose tracker system making your upgrade moot. Or you can lose upgrades when damaged, instead of repairable systems. You can in fact lose this tracker, which is the best use of it - be lost instead of something valuable.

So normally upgrades are received completely random. You download datacore, you get something random, and if you already had it you instead gain bonus battery recharge (+60s instead of +30s). However, for the upgrades game actually uses pseudo-RNG - upgrade received is defined by multiple variables. Changing the variable will alter what you should get.

Now, behold the secret. One of those variables is your current ammo count. Knowing this, you will suddenly find you have a very easy way of manipulating RNG. The only issue is that you have to abort the mission after undesirable result, then get upgrades again after doing manipulation - so trying to grind for early 2s download time will be very time consuming if you decide to. For the most part, playing the game the intended way is a better experience. But, at least you know what to do if you have next to none upgrades yet only get armory tracker and battery capacity from five cores.