MP3 is better!. As for wma it seems to be not as good quality sound as say mp3 or wav. But is ok for speech stuff.
So would I be correct in thinking that an MP3 song is a bigger file than a WMA version of the same song because it has more info that makes it sound better?
When it comes to size over quality, audio codecs are very diferent. Also the results are always subjective. Mp3 (LAME) sounds better because it uses a better rule set for handeling what stays in and what gets cut.