I have mostly MI (Marshall Island) and Fiji. A couple small pieces of Tonga branch.
Why? .... Well, let's see. When we set up our old 75g in Jan of '99, Fiji was pretty much "it" for available, reasonably priced
LR. I still like Fiji for it's coraline and amount of "life" on it.
When we set up the 180g, we added about 175lbs of Marshall Island to the existing 75lbs (or so) of Fiji. The MI doesn't have nearly the same amount of coraline or "life" on it, but it's worth buying for the shapes alone. It's also very porous and lightweight, and
IMO, because of it's structure, is great for water flow.
My couple pieces of Tonga branch and a couple other who-knows-what-they-are pieces, are just cool individual pieces I've picked up over the years. A lot of is it interestingly-shaped base rock that eventually turned into
LR.
I agree with RR re: the aquacultured rock. I've seen some gorgeous aquacultured
LR. However, being the wimp that at am, and having dealt with several nasty hitchhikers in the past, I balk at the thought of the Mantis, crabs, etc. that hitch along with aquacultured
LR. Not that you don't get nasty hitchhikers with other
LR, it just seems to be more common with the aquacultured stuff.
JMO -- oh - one last thing.
IMO, using a wide variety of
LR types is not only eye pleasing, but promotes biodiversity in the tank.