I really need to get into the habit of getting on the Org's channel. Most of my IRC use is sporadic as it is anyway (and by 'sporadic' I mean, 'mostly just for XDCC').
Client-wise, I use Nettalk about 99.9% of the time. Prior to that was Chatzilla, prior to that was IceChat. I've used mIRC a couple of times, but I really don't see the appeal of it. As far as I can tell, the main reason people recommend it - aside from simple brand recognition - is XDCC RESUME, and several non-nagware and FOSS clients now exist that also support that command. The reason I initially tried Nettalk was because it met those criteria: doesn't nag you, FOSS, and supports XDCC RESUME. Its channel storage features are also really nice.