Where you play poker is really up to you - there is little to differentiate the sites now as they all have thousands of players and it's really your own preference with the software or set up they use.
What i do strongly reccomend doing first is signing up at Royal Vegas Poker. Royal Vegas Poker are part of the prima network so the tables are always busy with plenty of other players.
So why should you use them first? The answer is simple - you get $10 free for signing up. No deposit needed at all.