Depends what format you prefer. I play cash on the iPoker network (I use either Titan or BSQ), but can"t find anything better than PokerStars for tournament play, both STT and MTT.
MTT Tournaments on iPoker are just a terrible structure..... any buy in less than $50, and you tend to get tiny starting stacks and fairly quick blinds, and no antes. The APAT and BSQ League games are ok with more chips and 15 min blinds though.
MTTs at PokerStars typically provide a larger starting stack (3000 for the daily $55 game at 20:00 BST) and 15 minute blinds, plus running ante"s from the 100/200 level.... they also include many intermediary levels (75/150, 150/300, etc).
STTs at Stars are particularly easy to cash in if you stick to buy in of $60 or less. My ITM rating on these is 75%+...... can"t get anywhere near that in STTs on iPoker or Boss networks.
Generally, the BOSS network is about the worst I"ve even seen. The play is usually very weak meaning it"s relatively easy to turn a profit, but the graphics are just awful.
At the end of the day though, you just need to hunt around and try a few.... you will discover which you prefer. I think I have accounts at around 20 sites now - typically I hunted for the bonuses and opened accounts to earn those bonuses, and during those intro periods I was able to determine where I preferred to play. Also, if you track your play either in a purchased package, or in a simple Excel workbook, you will soon be able to identify where you make profits and in which sort of game..... and that will help to dictate which sites you prefer to play at.
