Player and tournament volumes are approximations. 

Ease of winning -  based on how tough the players are in each room. The higher the rating the easier it is to win. Players call bets but raise and re-raise less. This doesn't necessarily mean the players are all weak. Most of the time I would rather play with a knowledgeable player (I don't mean a pro), than with a player without a clue. 
The weak, no nothing player ends up staying in with hands he shouldn't and ends up making a hand. He didn't know his odds were astronomically against him. I've lost some big pots to some of these players and there's nothing that gets your aggravated more.

Please use these ratings as a guide and check out the sites and make you own decision.  I play about nine of these rooms, playing them based on my mood and goal at that moment.

**Additional Notes on certain rooms-
PokerStars did at one time have some of the toughest players online but with all the new players they've received the tables have gotten a little easier. Has the most tournaments available 24/7.
Absolute Poker does not have the numbers of a PokerStars or FullTilt sites. But, does have some good games, average players, and plenty of action. You'll see a lot of the same players at the tables day after day which makes it a little easier to get a read on your competition. I play this room frequently. 
Doyle's Room is relatively new, has great graphics and it is a pleasure to play there. This site is constantly growing. You'll find a very diverse group of players from all over he world. Lots of European players. Remember, if you're in the States, there is anywhere from a 6 to 10 hour time difference with these players. If it's 8pm in the East Coast, it's 1am in London. You can sometimes use this knowledge to your advantage. 

GOOD LUCK

email me with any questions or comments.