There benefits to both MP3 and CD/MP3 Players...
MP3 players are small, but in order to have alot of songs at a decent quality, you have to pitch out quite a bit of money... I have a 128MB mp3 player and it can hold 44 songs but at a pretty crappy sound quality...
CD/MP3 players are well, about the size of cd's and play both formats... depending on the length of the songs and the quality, you can usually have over 100 songs at a good quality of sound...
So basically it depends on how deep your wallet is and how much you want to pitch out... because if I could afford it I'd get a MP3 player w/ the highest memory possible, and then have some extra memory cards w/ songs already preloaded...