Warrior: Anub - great mobility, lots of stuns, good damage. Closest next: Diablo for similar reasons
Assassin: none - though Kael is "ok", but I just don't like the role.
Support: Brightwing - cute creepy murder-voice, great abilities, awesome. Closest next: Tyrande. Great damage, stuns and no underwear
Specialist: Abathur and Murky, can't decide - both extremely fun to play and very rewarding