I mix. For larger setups, live rock is so expensive. So I like to mix it up and use some of each. You just can't beat that natural look of real live rock, plus it is needed for seeding. But dry rock works great for filler pieces. A few years ago on my last setup I bought a piece of man made dry rock that is in the shape of a cave. I love it, so do the fish. And eventually it looked exactly like the live rock. Just took some time.
