for music...go w/ Bearshare
I've tried D/L 'ing music from Kazza, I-mesh, limewire, etc. The best one IMHO for music is Bearshare. Reasons- w/ kazaa and limewire, they have bigger selections...BUT you get alot of 'fake' files (wrongly named) and alot of times you'll get this f*#king annoying 'hiss' after playing the song for a short while. I think some sort of sabatoge job from pranksters. In my experience, w/ Bearshare's file hashing/ verifying system, you get more reliabilty in terms of getting the correct file and usually higher quality playback versions of a particular song.
It's true that you get some ad-ware bundled w/ these 'free' p2p progs...but there's many ways to correct the problem.