Went through the last year using Pandora and loving it. Just didn't like not being able to listen to what I wanted when I wanted to - taking that choice out works well a lot of time, but when I am working I hate to break to constantly skip songs. I ended up with a few really well tuned Pandora stations that pretty much only play music I have picked.
My Pandora One subscription was up, and not having choice was a little annoying. So I decided to give the new and the old a try again and see what worked. Here's what I tried and I learned:
Napster - song selection was good, quality was terrible. After listening to Pandora for a year at 192 kbps, I was disappointed with the quality here.
Rhapsody - song selection was great, again quality was terrible. Rhapsody iPhone app was also decent.
GrooveShark - song selection was poor
Rdio - seemed to be OK, song selection was Ok, app crashed too often
MOG - quality was great, app was terrible. Crashed more often than Rdio's
Google Music Beta/Amazon Cloud Player - both were good, Amazon crashed occasionally, but both only gave me access to tunes in my library. I am a music junkie and wanted access to more.
Spotify - new to the US and have been trying the free version for a little over a month. Free version is good, but without iPhone and offline support, it's a pain. But with the premium version, I found a winner. Quality, song selection, local integration, application speed, device support is all good. I have had a few crashes and glitches with the iPhone app, but everything else seems to be great.
Not going to be stopping my use of Pandora for music discovery - it's great and has turned me on to many artists. But, I am going to be giving Spotify premium a longer term trial because I like to unlimited skips and to choose to listen to an album if I want. :)