I really like Pokerstars. 1500 chips, decently long levels, you actually still have some chips left at HU to play something other than the All-In coinflip game. UB has much the same format, though the games seem tougher.

I also like the 180 person, $20 SNGs at party. They fill up pretty quickly, so you can get in a good sized tourney pretty much any time you want.

PS SNGs do take longer though than a Party SNGs, so if you're trying to maximize the number you play per hour, I suppose go with Party.