iTunes is the worst MP3 encoder there is. Check blind listening tests done by hydrogenaudio.org - even xing, well known as being the worst audio encoder(they traded quality for speed) did better than iTunes encoded MP3s.
They also push AAC hardly so that they can push other players that don't support it out of the market - go figure.
LAME is the best encoder. Check around hydrogenaudio.org, --alt-preset standard is the standard you should use. It's VBR - the bitrate will change according to how complex the passage is, and it uses custom switches that you can't use just by screwing around with it. HA.org is like the NRC of psychoacoustic audio compression so to speak: I think you'll find a great wealth of information there.
