is it fast or is there lag cause I have a lot
of friends who say it'll probably suck . . .

Huh? The 3d fighters didn't have many or any complaints about lag that I heard of, let alone a 2d fighter such as guilty gear. There shouldn't be any troubles.

The lag sucks bigtime, and completely ruins SF3 on Live.
It may not LOOK like its lagging much (if you have a good connection) but theres just enough lag to through your timing off.

SF3 is too precise to play with ANY lag.

Otherwise the game is great.. Just get yourself a good arcade stick, playing fighters with d-pads is not much fun, and the xbox d-pad is worse than most others.

Ive heard guilty gear lags too, and SvC:Chaos has terrible lag. I havent played any 3D fighters online so i cant comment to them. Id rather play Virtua Fighter 4 offline than DOA online anyways.

I enjoy SF3 online, even though there can be the occasional slight lag against some oponents. Hyper SF2 on the other hand, I find unplayable...