MP3 and Redbook audio (CD audio) are both data, they only differ in the ordering and composition of the data. There are also hybrid discs which are redbook, but track one is the data. This is how many games used to be distributed (see Interstate 76, Mechwarrior 2 etc), and if uyou put them into a cd player and played track one it would be either skipped or loud modem-like noise.
A CD holds approx 700MB.
If you are burning the Redbook audio from mp3 sources, You are upsampling and decompressing (and replacing lost data) which gives you nothing and therefore it comes down to capacity.
So the capacity you really care about is the music itself. In human terms without data rates etc., a redbook audio CD holds about 1 album's worth of music. (about 70 minutes)
A "normal data disk" with MP3 files in a folder structure can hold more than that. It varies by encoding and song length of course, but you can expect to be able to burn approx. 5-7 albums to it.
So which do you prefer? One album per disc or five?
Note that some embedded audio systems (like in cars) do not have perfect mp3 decoder support, so if many songs in your library have an encoding that the car chokes on, then the Redbook audio would be a better choice.