facebook AND myspace. Facebook is rubbish for uploading music, but there are many great solutions - try going to bandpage.com. It is essentially a music player for your facebook page. Its very reliable and you can either upload from your pc or take from soundcloud.
Myspace should be fine with mp3s. Make sure your songs are set to public. It is probably also best to have them in 128kbit/ 44.1Khz format
There is also reverbnation, bandcamp and other sites...they all pretty much do the same, and they all do the same as purevolume