Lieutenant: Heat Ammo (50% extra damage against the toughest enemies in the game - an easy choice).Sergeant: Shredder Rocket (this gives you more rockets and allows you to take down bigger enemies faster).Corporal: Bullet Swarm (allows you to attack twice in a turn - extremely useful).Squaddie: Rocket (the Heavy's bread and butter).For abilities, I recommend you take the following: Their accuracy isn't extremely high, but they can fire a rocket launcher, giving them far more damage.