I think Myspace is very popular because you can get a site that's very memorable for people. Like mine is
www.myspace.com/larrylevin. If you have a band page, other people don't have to be myspace members to enter your page.
I use two sites because once in a while someone complains that they can't hear the audio. There are always glitches with one site or another.
The other site I use is
www.reverbnation.com. I wouldn't use reverbnation alone because once in a while people can't open their player if they have their pop up blocker up. The good thing about reverbnation is that it gives you very detailed stats. Also, you can get an app for your facebook page and have a player right on your facebook page.
Beakybird