Sounds as though you're happy with what you've found music-wise, but if you're still looking at other options, may I point you to slacker.com? For me, their "build your own" stations have proved far more satisfying than Pandora's. I've built four so far, and listen almost non-stop. On the other hand, if Pandora is extremely good at sussing out your preferences based on your seeds, I guess there's no reason for you to switch. I just couldn't seem to get things synched with their algorithm.
BTW, slacker also has a fair selection of pre-built stations.