Rise of Pheonix. Although (as i'm typing this) the server is currently down to a technical problem on the dedis side of things, the team are great and the server is growing rapidly, although still in it's 'early' days.
The server deserves more recognition, more players, and more player input, although the user count has been pretty good lately. The work i have seen Lilcooldoode testing lately is outstanding, some i've never seen working on any other mir before. Almost every single bug I've reported to these guys has been addressed if not fixed within a few days, and to top it off.. Iceman is just a really nice guy.
This, along with some great new features whilst keeping the old school feel.
Check the forum under the server section