Your right Ben...you can currently fit about 20 audio tracks or 80 minutes onto a CD which are .WAV files but you can fit apporx 200 mp3,s onto a CD the disadvantage being of course that the will only play on DVD players and Computers....though i believe some modern CD players can handle this most won't.
It depends on what u want to use the cdr for. If its just for storage then use MP3, but if its for playing music on a cd player, the you'll have to use wav files.