I had been using Slacker, but I'm enjoying iTunes radio. I will not renew Slacker in the fall.
I love Slacker but would be joining you if iTunes Radio wasn't still so buggy for me. It plays songs I've chosen to block. It plays the same songs repeatedly within a short span of time. Why do I hear Money for Nothing (which I love, don't get me wrong) almost every time I fire up the Classic Rock station? Surely there are enough songs in that catalog to prevent that obvious a repetition. Songs with explicit language slip past the filters (granted, this happens to me with Slacker as well).
Apple needs to polish up some of these basic functions before I can use iTunes Radio exclusively.