That depends on what kind of fish you want to keep. If you want to keep altum angelfish, the higher tank is better. For long-bodied fish, a greater turning radius (i.e. the deeper tank) is better...
i have a silver arowana and parrot fish, so i guess a 4x2x2 but it is not my arow so forget that i have him (ill have him upto about 10inces) , i just want what you guys think is best, for SA and CA cichlids, ie GT's JD's and severums