I like Pandora better. It seams to do a better job of taking my likes and dislikes to build a great custom station. I've only used Slacker on my phone, but Pandora does a great job working across many different devices with the same experience
Last time I used Slacker the music quality was terrible, sounded like crap. Not too happy with Pandora either, but at least it was better than Slacker. I do like Slacker's music better though. I'm always on Slacker from my work computer.
I use both.... Slacker has more structure to each type of music and offers 171 channels including news and sports. Pandora is kind of cool due to the more free form style of music. I play them through my phone with a Blackberry Gateway for the car, through the phone or my laptop through a Creative Labs 3.1 system on the back porch. I also run Pandora through my Roku box through my home theater stereo system... they all sound the same to me. With Slacker you can skip as many songs as you want, with Pandora you're limited to 6 skips an hour, but you can always jump to another channel. Now that Pandora offers comedy channels I might be dropping Slacker.
Are you hurting for space on your phone? Why not keep both on? I keep Slacker, Pandora, iheartradio, and tunein radio all on my phone. Different situations will have me using each so I just keep them all.
I wasnt aware that Slacker was bloatware and couldnt be uninstalled. I played it for over an hour today and it was ok. I've been using Pandora for much longer and wondered which was better.
No way I'm hurting for space - I doubt I can fill this phone with apps.