Why " live " rock from GOM is better?
There are two fundamental schools of thought on this. One is the "quarantine and sterilize everything" school. The other is to get as much biodiversity in the tank as you can (
@Paul B is probably the extreme example of this) and let it work itself out. The first school makes intuitive sense. However, many of the most vocal advocates of the last school have a lot of experience with the ocean (again, to include
@Paul B, whose family worked in the seafood business in NYC in the 50s, and due to this and his 40+ years of marine aquarium keeping he probably knows A LOT about handling ocean livestock).
I'm not aware of any empirical tests showing the long term advantages/disadvantages of each side. I do know John Tullock, a prominent saltwater aquarium writer who apparently passed several years ago (who had a PhD in marine biology, did lots of field work in the Keys, and ran saltwater aquarium stores from the 60s-90s) said that ocean live rock will be better because (paraphrasing) it's a tricky and slow process to bring dead rock through the nitrification -> denitrification -> diatom-> cyano -> finally coralline algae phases. In his experience, lots of algae problems are a result of problems in that cycle. (even after two years, my dead rock has minimal coralline growth, while my ocean rock has persistent patches of coralline and sponges that expand and contract).
And as far as the GOM live rock, here in the U.S. people of the second school will generally prefer live rock from the ocean. The GOM has a few live rock farms, and several vendors (like
@liverock ) will ship it to your nearest airport, with water, same day (it's as if someone took a fish from the Mediterranean for you in the morning, and you picked it up at your nearest large airport in the afternoon). This IMO is far and away the best way to get real ocean live rock, if that's your thing.