I have Garrus with either a Widow, Javelin, or Black Widow I give him the Sniper Rifle Damage upgrade at Rank 6 (the power one at level 5 resulting in weaker assault rifles in exchange for a higher damage Overload)
Those 3 Weapons combine fantastically with Cryo Ammo, they also happen to deal excellent damage.
Someone else would have to help you with Assault Rifles as I don't really pay attention to those with Garrus.
"Badassfully You Big Stupid Jellyfish"- Bubin, Mass Effect 3
I give him, Ashley, Javik, James the particle beam. I always use it too much and wind up burning it out and having that long cooldown because I'm wanting to just get that last bit of high intensity beam to fry off my opponent towards the end of the clip, and always wind up with it empty. AI characters, however, absolutely fry stuff with that thing.
Mass Effect 3 (360) Uncharted: Golden Abyss (VITA) Skyrim (PC), Dungeon Defenders, Angry Birds (AND)
I was wondering the same thing...I figured I'd give him the Black Widow so that way even if he misses the first round, he'll be able to get another shot off without having to reload after every single shot.
But...how good are squad mates when it comes to sniping in ME3? In ME1, people swore by a Sniper Garrus *mine was always AR* so I never saw if sniper garrus was epic.