For Mac OS 8.1-9, LimeWire is the only choice.

For OSX 10.1, LimeWire

For Jag and Panther--LimeWire
(my kids like the interface Acquisition puts on LimeWire)

LimeWire has more developers working on it fulltime (they often post here in the forums too), and a goodly group of open source developers who will help out and have even added special patches. Since gnutella is a dynamic network and its development is dynamic, you want a client that will keep up with whatever changes happen to be implemented each week.

There is currently no spyware in LimeWire for OSX, but if you are nervous, Jens-Uwe Mager regularly builds an equivalent to LimeWire Pro that he offers freely http://baghira.han.de/~jum/LimeWire.html

As Arne said--share. LimeWire is my choice, but I support Acq too and plan to support Phex when I get a chance to try it.