well, i sort of stumbled upon it, so this isn't a scientific comparison of all possibilities -- but here goes.
1. It is well maintained, robust and easy to use
2. It provides helpful statistics
3. I like the player -- it can play lo-fi for dial-up as well as hi-fi for high speel internet
4. you can upload photos, add links, movies, news, etc.
5. you can easily offer pieces for download (for free or for sale if you have a paypal account) -- but this has not been lucrative for me personally, i don't know about others....
6. There are charts so you can get an idea where you stand in relation to others writing similar kinds of music
I wish I could upload scores to go with the music, but Dave (etLux) told me about Lulu.com, so I will be directing people there for scores as I get them cleaned up and put on lulu.