Vagabond, by far. He was the only main wingman who didn't have... issues.
He wasn't a rookie (Catscratch), he wasn't crazy (Maniac), he wasn't a complicated love interest for Blair (Angel), he wasn't a simple love interest for Blair (Flint), he wasn't a traitor (Jazz), he wasn't a traitor (Hobbes), he wasn't a pacifist (Panther), he wasn't gun-happy (Hawk), his hate didn't consume him (Cobra), he wasn't arrogant (Flash), he didn't have piles of emotional baggage (Spirit), he wasn't a cold motherfscker (Iceman), he wasn't an irritant (Maestro), he wasn't all pessimistic (Doomsday), he wasn't raised by the Kilrathi (Downtown), he didn't pick fights (Stingray), he wasn't an inexperienced reservist (Shadow), he didn't tritely talk about opening a bar after the war (Vaquero), he used proper grammar (Excel from WC4, I think it was), he wasn't old (Paladin), he wasn't a faceless name (that one wingman guy in Armada), he wasn't a sick b*stard (Seether, remember flying with him? brrr), he didn't drink too much (Hunter)....
I can't think of any issues surrounding Bossman or Knight. Or redshirts like Primate (who r0x0r3d). So I guess they're cool too. But not as cool as Vagabond.