There has been one area of quality missing from this thread. That is how to best make the MP3 you can. There is more to good MP3 files than just the bit rate used.
http://mp3.radified.com/ contains some very good information on creating quality MP3 and has links for addional information. It even discusses lossless compression too.
If your going to make MP3 files you might as well make a good ones.