Loadout:
Sniper Rifle / Vektor Rifle
Pistol

Squaddie:
Squadsight
Snapshot (take a sniper shot after moving but has an aim and crit penalty)
Fire Pistol

Corporal:
Mark Target (Mark a target, granting allies +15 aim against them)
Phantom
Longwatch

Sergeant:
Quickdraw
Aim
Steady Hands

Lieutenant:
Deadeye
Deadshot (+10% crit chance)
Cool Under Pressure (+10 aim and overwatch shots can crit)

Captain:
Clutch Shot (Pistol shot with +100 aim, can use squadsight but can also miss with squadsight)
Deep Cover
Interupt (A powerful form of overwatch that lets you perform any action instead of firing)

Major:
Weapon Expert (+2 dmg with primary weapons)
Hide (Re-enter concealment at any time, has cooldown)
Seek & Destroy (50% chance to fire at newly revealed enemies)

Colonel:
Death From Above
Serial
Kill Zone

GTS:
Focus Fire (+10 aim and crit chance)