Harvey. Josh was kind of meh. Aaron, well, I was just rewatching some of the later episodes and there's one where Aaron takes care of Salem while Sabrina is away? And he treats Salem horribly! Locks in him a little cage and everything! I realize that Salem can be a bit of a pest but man, anyone who treats animals like that is not cool in my book. I mean, even if he doesn't like cats, he's Sabrina's pet. You'd think he'd treat Salem well for that reason alone, if nothing else.
Harvey took good care of Salem when he watched him, he was always looking out for Sab and he still treated her great after finding out she was a witch (after the initial probs, that is). He just wanted her to be happy. So yeah, gotta go with Harvey.
It's not about who you are or your fancy car. You're only ever who you were.