I upload to both reverbnation and soundcloud. I prefer reverbnation because I get more listens there plus I like their media player which I have embedded on my main website.
In addition to allowing you to update an existing mix, the paid "Pro" account on soundcloud allows you to upload more songs (6 hours instead of 3 hours) and more detailed statistics so you can see who is listening to your tracks, what country they are from, etc.
But there is no reason to stick with just one platform, you can create free accounts on both and that's definitely the best way to get started as Noel recommended.
Also, if you want to get featured on pgmusic radio you must have a soundcloud account, although they haven't included any of my songs there for a very long time. I guess no one at PGMusic likes blues music