Regulus
Have you ever spoken to him? I've been stuck in a car with him for weeks, and he's at least got good manners. More than I can say for Potter Though he was very kind to me the other day.
Sirius still shouldn't be living with him though. It's not like he needs a roommate. Unless he's squandered Alphards fortune already, which I just admit does sound like a very Sirius thing to do.