I'm pretty much on Freenode most of the time, though it generally runs either detached on my home server (using screen) or it's minimized. On Freenode I mainly frequent #hamradio, #macosx, #devious (for devio.us unix shell service), and a few others depending on what projects I'm working on. I used to hang out on Efnet and Undernet years ago, but it just became harder to find good conversation on both networks. Freenode always seemed more friendlier, IMO anyway.