Know this is a bit of an older thread but for the price, customer service, and sustainability aspect, I'm going with addictivereefkeeping in the next month or so for about 500-600lbs of rock. If you look at the flat shelf rock on the site, you can't beat the price per pound and for anyone looking for stax type rock without the price tag, buy the large pieces and use a chisel to break them into smaller pieces. Considering 90lbs of pristine flat shelf rock is only $269, it's a no brainer. Can't get near that anywhere else. Their small, medium, and large prices up to 150lbs definitely isn't too shabby either.
Just my 2 pennies worth