1) Party and skins (Empire...etc...)
Sheer volume of players makes game selection much easier. Some very fishy play. Good SNG tourney's, although blinds go up quick, they are a moneymaker.
2) Stars
Ring games are ok, but you will play a lot of the same players. #1 tourney site for multi table events. Good customer service.
3) Ultimate Bet
Ring games can be great or terrible, depends on the day. Mini-view for multitabling is good. A lot of bonuses, but sometimes slow to clear.
4) Pacific
Site just sucked. The only reason they are #4 is because I've only played 4. At the time you could only play one table. Slow cashouts as well.