I was running a 25g that was 12in depth. If you are selective in your fish choices there is no problem that way, but I found it a nightmare to aquascape. By the time I got my rockwork arranged, there were spots I couldn't get my cleaner magnet between the rock and the front glass.
That tank was only 30in wide and I didn't think one MH covered it properly. It worked out ok though, as I had the MH to one side lighting my clams, and the dimmer side was good for lower light softies.
I vote for the 36in tank, or better yet a 75g like was mentioned previously (which is what I did)
Marcel