I prefer Audiogalaxy for searching for mp3s. I prefer to rip my own monkey's audio tracks, but when looking for new music, mp3 is the only way to go. I just deal with the 128k crappiness most everything comes in.
Why Audiogalaxy? It has an extremely supeior search setup. Of course, this is only if you want the most common version of each mp3 and they are usually 128k, but again it is good enough to listen to the music for what it is. It automagically queues everything, you don't need to worry about what users have it at all. Transfer speeds can be excellent. The auto continue when a user disconnects is great, because on AG specifically, there will be hundreds of others with the same file on their PC and because AG is centralized you get it automatically, and are dealing with a much larger user base (Whereas on the p2p apps you are dealing with a small subset).
Problems with AG: less high quality mp3s, only 10 simultaneous downloads (But you don't need to think about anything at all, they queue up automatically and download when they can. Optional spyware on install if you aren't careful, interface is ODD.