This is not meant to be a general discussion of mp3 vs. RealAudio, since they are for completely different uses normally.
It is intended to be a guide to what to choose when visiting Indie Online.

mp3

pros

• Sound is near CD quality

cons

• Has to download large file before you can begin listening to it

RealAudio

pros

• streams from the website, meaning that you can listen to it while it is downloading

cons

• low soundquality compared to mp3

Bottom line

You might want to start by listening to the RealAudio version of it to get an idea, and then download the mp3 if you want to hear what it sounds like "for real".