I've heard that aac is better. However, it has little support.
One note of caution, though: MP3's are a lossy (sp) compression format (you loose quality in the compression.) So reencoding MP3's as something else would still give you a lower quality music file. I personally don't think converting a music file to another format can enhance it.
If you rip the track as aac, then perhaps you might notice an increase in quality.