What are the differences between the major online chess sites that allow to play? I'm thinking of dedicating some of my free time to learn and play chess in a systematic and serious way and try to participate in a non-Internet tournament in a few months. I will take this activity as a hobby, but still want to keep it serious, cos I know that my progress will determine how much fun the thing will be.

I know that there are many websites that allow you play chess online, but I'm interested in what experienced users have to say about them taking in care my goals. I'm looking for a place that allows me learn, play and test myself giving me a kind of rating from which I could infer with more or less accurateness my FIDE ELO and then decide when I'm ready to spend time participating in a non-Internet tournament.
Nowadays there is really a abundance of good chess servers. And they are all relatively similar. I think you need a site where you can:


Play blitz chess
Play correspondence chess
Do tactics training
Learn via articles and/or videos


If you want everything on one site, www.chess.com is probably your best bet. As far as I know ICC, chess24, playchess and FICS don't have correspondence games. For beginners it is often hard to play blitz, and even later you might learn more from longer games.

The downside of chess.com is that the players are relatively weak. But if you are just starting out, this is not going to bug you for a few years.