You should definetely create a Pokerstars account through Pokerstrategy. Strategy is the only place that gives you some extra benefits, every other site only gives you 1-time freeroll. That 600$ dep. bonus is easy to clear as long as you make 3 different deposits and split the bonus. If you make one 600$ deposit, it is very hard to clear as you have to clear all of it before getting anything. You have 6? months to clear it though.
Pokerstars has toughest games on average, but it also offers most games and players, so you can pretty much play anything you want whenever you want. You can also do a lot more table selection here. Pokerstars is also the only place where can open more mid-stakes Sit and goes than you can handle.
Even though there is no rakeback, there is the vip program that will give you 10-20 percent back (and 28-40+ % if you make supernova/supernova elite) + first deposit bonus without any reductions.
There is another good thing on stars; the rake is a bit smaller as it is taken in .05 increments. Let's say you win 0.50$ pot. You pay no rake for that pot, while on other sites you would pay 0.02$ rake. Or you win 6.90$ pot. Now you pay only 30 cents of rake instead of 34 cents. That adds up fast.
Stars also has the best software (just my opinion, some people prefer Full Tilt) and it is the best software for multitabling.