if you plan on being a regular player I suggest you to sign up to a poker site through a poker affiliate who offers rakeback...
rakeback gets you back a percentage of what you pay in rake to the poker room, these "refunds" are made weekly or even monthly
unfortunately pokerstars does not offer any rakeback under any circumstances, neither does doyles room anymore....
i suggest you to try fulltiltpoker, absolutepoker or ultimate bet, those have the biggest traffic, and offer bigger tournaments.
for poker affiliates who can get you rakeback i suggest you to try pocketfives.com, pokersource.com, thisisthenuts.com or rakebreak.com... that way you will be setup for rakeback and you can play on monthly freerolls or compete in rakeraces.
ultimately, you should try most of the poker rooms, only then you will decide which one suits for your preferences... everyone has preferences of their own and it depends on which games and limits you prefer to play