I love my 30 inch cube, only downside is a sump in the stand can be difficult to design or find while trying to maximize the water capacity, but once you figure that out they are awesome.
I figured a sump would be an issue, small one only if I had recommended a 50/60 gallon cube. I made a few months ago a sump out of a 30g tank, shortened the glass a few inches and added baffles.
Now that I have the proper size cube, I'm going to use a 36" long sump that has been in the basement for a while or use a 40B; that will be decided when the stand has been completed, nothing fancy.
Here's my 36 x 36 x 24 Leemar. I've like it a lot. Biggest struggle has been figuring out the best method and placement for my vortech's. Most places I would put them will put some coral (acros) in direct flow from the power head which doesn't really work well for most acros in my experience. Currently have 1 mp40 on the back left, one mp40 on the front right, and 1 mp10 on the back right. This current set up creates a lot of flow on the front left corner of the tank. Still trying to figure out the best way. I'm intrigued by the poster that is using the gyre's vertically.
One of my concerns is the flow for the cube but since the cube will be in a basement, looks are not important. I think to have a couple of MP40's, at least that's what the box in storage is labeled.
A friend of mine is getting rid of his Leemar 36 cube; what drive me into buying a DD 36" cube, was his setup with a single Lumenarc reflector centered over the tank.
I still haven't had the time to build the stand, did cut some wood but that's about it, tank sits in the basement waiting, in the mean time I have a 50g drum tank filled with rock and water from two different systems to "seed" the rock.
Maybe when the rains come and work slows a bit, I'll have some time to put the stand together...