Soulseek is by far the best. No adware or spyware or any shit like that. Its fast & reliable, very easy to use. I've been using it myself since about 2005 & have never had any problems with it.
I tried Kazza, Winmx, Limewire, Bear Share, eDonkey & a lot of other p2ps but none of them compare to soulseek.
It's free & very safe to use.