Weapons: Shotgun / Rifle / Smg
Secondary combat knife

Their skill selections are broken up into Melee, Shooting, and Utility by row - you can mix and match as needed, or you can go with a dedicated single row build. I tried to keep picks competitive at every level, but the meta of your environment and your play style will likely favor a fixed selection. Defensive players may really appreciate having a more ambush based build, while aggro players might like focused shooting or grenades; in a pinch the freebooter is a passable dedicated melee, and the xcom row can support a lot of different applications.


Squaddie:
Collateral Damage (collateral_lw)
Dedication

LCPL: Lightning Slash, Focus, or Rapid Deployment
CPL: Cutthroat, Run and Gun, or Total Combat
Sgt: Combatives, Marauder, Watch them Run
Ssgt: Fleche, Ventilate, Sting Grenades
Tsgt: Whirlwind, Hit and Run, Implacable
Fsgt: Shank Redemption, Coup De Gras, Devastation
Msgt: Reblossom, Fearsome, Iron Rations

The overall idea is to use them to break up stalemates - moving through contested areas with dedication to deliver some single target damage to a key threat or leverage grenade skills to impart some aoe impact.

At msgt, they can be deadly knifers, excellent flank shooters, or dedicated grenade slingers; but will probably be best with a mix of abilities from the columns supported by some strong xcom row picks

On the Xcom Row, they do have access to a lot of abilities can provide buffs to their primary applications - things that give bonuses to melee, shooting, or grenade use, that may influence your intended build - and this is by design to keep freebooters feeling like they can slip in and out of different squad compositions and add value - but always with the aim of being a 'mid tier soldier' - not hogging all the action, not a definitive specialized soldier, but always useful on a roster.