Upon returning to chess after a 15 year hiatus in 2004 I tried several server sites and here’s my impression of the ones I played on.
CCLA- The only CC organization worth mentioning for US players. They offer post card play if that’s what you prefer. They have only recently gotten into server play using the ICCF’s site. In addition to club membership you have to pay additional EF’s for each event. If you play a lot it can get pricey. Has many strong players (many also play OTB) You join at your USCF rating. If you don’t have one you can estimate it up to 1800. It’s the official ICCF representative in the US.
Red Hot Pawn. This was the first site I played on. Limited number of games for non-subscribers. If you’re a non-sub most members won’t bother playing you. You start out at a low rating (1200?) so I won something like 20 games in a row and was only rated mid-1500’s. OK if you are lower rated, I guess; no fun if you’re not. Forums can get real nasty. They are constantly on the lookout for engine users. I saw 1200’s get kicked off the site as well as a bunch of their top players. They claim to have an infallible method of catching them. I have mixed feelings about this site.
Plasticbishop. Free. Lots of beginners. Of my dozen or so games there the longest was 22 moves; the shortest 5 moves. Good site if you are a beginner. Not much goes on in the forums.
Queenalice. Probably the best free site. I only played a few games there and had opponents from 1200-1800, so it wasn’t too bad. Not much goes on in the forums there either.
Chesshere. Limited free games. They also offer real time blitz. GM Amir Bagheri (or someone claiming to be him, I won’t get into that) took over the site about a year ago and unless you subscribe, be prepared for a ton of annoying pop up adds. You have to play a hundred moves or something before you can post in the forums. Personally, I’d avoid the site.
IECG. Free. This is a very large server site out of Germany. They try to emulate the ICCF by offering (meaningless) titles. You have to verify your rating when signing up. Your number of games are limited when you first join. Mostly tournaments. CAUTION: They have no rules against engines and everybody uses them. Don’t think you’ll get a top rating there using Fritz or Rybka. Their top players ARE able to play well enough that they know how to play against engines and win.
Chessworld (aka Letsplaychess). The only site I belong to these days. You start at 1400 officially but your first game will be against a welcoming opponent who will be rated close to your estimate of your ability and answer any questions. This means you can quickly establish a higher rating (if you win, of course) and play stronger opponents. The site has a ton of training features for members; limited features and game limits for non-subscribers. Plenty of individual matches and tournaments are always available. Forums are very friendly and helpful. They do have one GM and many players are Europeans known to each other and have verifiable FIDE ratings. I also know of at least one IM who plays there. This is my site of choice.