Basically I'm wondering what the best cross-platform shooters are for competitive gameplay. I use linux so cross-platform is a must, I'm not bothered if it needs a loki installer or a cd, or steam but I prefer cd's with official installers.

So, I'm thinking about getting the following:

CS:GO (steam)
Earlier versions of CS (cd + loki installer)
Quake 4 (cd)
Doom 3 (cd), have a feeling it's not competitive.
UT2004 and the new UT when it has an official release

Also happy to pick up any quake or CS style games if they're still being played competitively.

I'm currently playing urbanterror casually and I'm wondering if anyone can comment on if it's still popular at a competitive level.