Difference between chess.com and other correspondence-style web-chess servers?

Does anybody here know what are the major differences between chess.com "online chess" and the other correspondence-based web-browser chess servers?

I like this place very much and intend to make this my primary place to play. However, I am looking for other variants too like crazyhouse, bughouse and time controls that are based on time per game (as opposed to time per move). Something like a fixed 30 days per side for the entire game would be nice.

I don't know

We aren't meant to advertise other sites on here, but seeing as you are wanting to make this your primary site I'll mention one other.  The site using most variants is probably www.schemingmind.com but their interface isn't to everyones choosing and number of users certainly a lot less.