(Note: According to the achievement descriptions, you're fighting with 'avatars' of your friends.)
Hraesvelgr - Midgardsormr finally got him to work on himself so he wasn't such a sad sack, and we get to take him adventuring with us. He spends most of his time muttering under his breath and blocking the camera. Soon voted least favorite trust.
Baby Midgardsormr - All he does is fly behind you and make sage remarks about the folly of man and how weird mortals are.
Alpha - uses his cards in battle! Also randomly makes you invisible.
Nero - Smugly tells you about all his latest gadgets/improvements. Makes fun of you when you die.
As for young G'raha being a possibility, I agree...but he wouldn't be an all-rounder, I don't think. He was originally an archer, which just means having a fourth DPS. They'd have to figure out how to change his job, I guess. He sure won't be throwing out benediction in between flares like Exarch.