I've only be using the first two options for a week now, and I'm certainly I don't have all the ins-and-outs figured out. I just opened a Reverbnation account today. Still, they all have different advantages and uses, so here are some of my thoughts into the process.
A nice place to start. With a basic subscription I was able to upload 2 hours worth of music, join groups and share my music with friends, family and other artists. There is a limit of only 3 sets (playlists) of music, but a workable limitation.
I only joined 11 groups and posted a piece to each one, so several of my pieces didn't get posted at all. I also posted links to the pieces (or the sets) on facebook and twitter. The end result is nearly 100 plays in just a week.
Top songs are
Easy on the Tonic performed by Reggie Berg: 15 plays
Taken for Granite performed by the Edinburgh Quartet: 11 plays
Piano Prelude 3 performed by Ani Gyulamiryan: 9 plays
Trusting performed by Reggie Berg and Drew Rackow: 9 plays
Osculum Pacis performed by Firesign: 9 plays
5 songs have been downloaded and a couple of people have commented. Most of the plays have come from the US, but there are the occasional "fans" from Sweden and UK.
Spotify doesn't have the same kind of stats but it does have a sizable following beyond musicians. It's huge in Europe and just coming over the the US (currently in beta). I can't tell how many people have played my music or even get comments directly back - but I have received some comments from people via email or otherwise who mentioned they heard it on Spotify.
Like SoundCloud, Spotify has different levels of participation. The "free" version doesn't allow the music to be online unless I'm actually online and connected -downside. BUT, the $4.99 a month version does. No, I haven't upgraded (yet)...
Another nice feature of Spotify is the vast number of uploads already in play. If you're a music lover (and not just a composer or performer), this is a great way to get access to lots of music.
As a musician this one is particularly nice as it allows up to 8mb files to be uploaded. Ok, Chasing Dark Matter Galaxies had to be redone to be a bit smaller, but it's 10 mins of orchestral music!
Musicians, you can also create t-shirts, mugs and other "fan gear" without the cost of purchasing the t-shirts and such ahead of time. Reverbnation also submits your music to iTunes, Amazon, Spotify, Last.fm and more - but you have to pay for it (surprise!).
So, for the indy artist this is a pretty good deal; I should have created my account some time ago!
Wow, that was a chore, uploading music, selecting merchandise and trying to get my profile put together. It's not done, but then self-promotion is never finished...