You’ve got it a little mixed up about the networks.
Kazaa, Kazaalite, Imesh and Bearshare use the FastTrack network.
Morpheus, Limewire and a few others (including Shareaza) use Gnutella.
WinMX uses its own network. Which has recently been shut down by the RIAA, but patches have sprung up in a matter of hours to redirect it to another server list that works just as well.
Anyway, in my opinion the absolute best p2p program is Reverse connect. It uses the Direct connect network and is a modified version of DC++, allowing multiple downloads.
The DC network is divided in many hubs, each of which has a minimum share.
Its main problem is that most hubs have very high share requirements. It’s not uncommon for them to want 60+ gigs.
There are hubs for people who don’t share much (3/5gb), but if you don’t have anything at all you probably want to get some stuff first.
RC is very good for music of all kinds. If you share a lot and can connect to the hubs with the largest numbers of users you’re very likely to be able to find rather rare stuff (though you’ll probably wait a while for it to download, as they are rarely shared by more than a handful of people). It’s not as good as Audiogalaxy was back in the day (with its centralized servers connecting ALL users and their files at once), but it’s close enough.
It’s also very good for movies and games.
If you’re looking for particular versions of some files, or full cds at once or older games, you may like BitTorrent more. It requires no share, which is a big plus if you don’t have any. You should still allow other people to download from you. Hint: the most straightforward client is BitTornado.
If what you’re looking is REALLY rare, or if you’re looking for exotic downloads (books, parts of local tv shows, etc) you may find eMule to be better. It requires a great deal of patience to set up, and lots of time and sharing upload (preferably an always-on connection as well) to work correctly. It’s also known to be rather slow in downloading. Personally I exhausted my energy after a few minutes and have never reinstalled it again, being happy with RC/BT.
Your mileage may vary…
More than everything, remember not to leech without giving anything in exchange; p2p networks work because people share. Faking your share or using other hacks to avoid other people downloading from you is the worst thing you can do (and will probably get you banned from DC hubs).