Kharjo is probably my favorite.
J'zargo is also pretty cool.
Wish Kharjo was romanceable too. He's a sixy kitty. Ah well.
His quest is pretty great, and he has a lot of personality. Plus, since my character doesn't use shields or heavy armor, he gets all those fun toys instead.

I'd say any special ability for him should be related to his talents with a shield... or something related to his dialogue line: "If anyone sneaks up on us, I'll smell them coming. Or, I might not, we'll see."