Yeah PokerStars has a lot of tournaments with a LOT of people that makes the 1 and 2 dollar tourneys worth the effort. The 3.00 rebuys are fun and pay off well if you make the cash.
The 4/10 and 20 90 player SnG's are good for building an MTT bankroll.
Although Full Tilt has a pretty good tournament line up too, their deep stack SnG's actually give a player a chance to PLAY rather than push their luck. Not as many people but again the pay out is worth the effort.
Absolute Poker has a lot of freerolls
and is a good practice site, (at least for me) Small field MTT's the payouts can be small but an experianced player can beat their MTT's and make some final tables. Yeah I'm saying AP is soft, their are occasional sharks but the aquarium is full of edible pescado.
Ultimate Bet ....I find this site is rather a chore to navigate, the tourneys are not very full and the pay offs small to medium. Why do I play there? LOL there's really only one reason I do .... I win there ... heh heh
Bang for the buck though is Poker Stars, lot's of action but it's infested with sharks, but that's a good thing, you're only as good as or better than your competition. Schooling sharks ... tis impressive.