so ive been test driving a few of these services. heres what i came up with:
first off...all these services let you create stations like pandora. while pandora depends on that its just piddly feature to these other services
slacker - i could search artists or albums, play anything i found on demand. i understand that there are restrictions because of licensing but i didnt run into any. i could create playlists, but i didnt see a way to keep an actual library. admittedly i only used it like 4 times, maybe 2 hours each time. the best feature for this service is being able to save stations and playlists to your sd card to use offline. its voodoo, i tell ya. i paid for a month so more impressions later.
songza -best feature is that its free, but its only...like...a playlist service or something. its ok i guess but way outclassed in this discussion imo
music unlimited -ive been using this the most. i love it. its almost exactly like slacker except you cant save stations. you can save playlists tho. another thing i didnt see in slacker is that you can listen to a station ("channel") and if a song comes up that you like, you can add that song to your library, or add the whole album. you can build your library like itunes but no housekeeping at all. they also have premade channels, some similar to the mood playlists in songza, some by genre, some by era. i mean this shyt is laid out breh. heres the best part - i can use it on my iPhone, xoom, vita, macbook, desktop, and ps3. the issues i found are sometimes they have server hiccups. they also give you a 60 day trial if you get it thru psn.
i think my personal choice is already clear...tho i plan to check out the spotify trial soon to see whats good...