I personally like Marshall Islands liverock the best.
I hear that Kaleini is good.
Tonga branch is pretty neat too.
Aquacultured Gulf rock is nice in regards to color and life.
Best price cannot be discussed because of board policy - but honestly, it really depends on what you want. That - and it's such an important part of your reef - do you really want price to be the only deciding factor?
I mean, you pay so much for other things - why skimp on the liverock?