Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I would certainly go toward the taller end of your choices.
I have a 40 gallon breeder that is just about what you are thinking about. 36" x 16" x 16".
It is one of the easiest to 'scape.
The depth front to back allows much better layout of rocks and driftwood so the tank really has a 3-D effect. I have quite a few other tanks that are from 12" to 15" front to back, but taller. (many are 45 gallon, 4' long) They are harder to scape because they are not that 'square' sort of ratio. The hardscape elements need to be aligned parallel to the tank, and this sort of flattens the whole effect.
On the other hand, a real cube tank (all 3 dimensions the same or really close) offers some challenges, too. They can become really impressive layouts, but it takes skill to make them work.
A shallower (height) tank such as your lower options would limit a lot of plant choices, and the 'scape would either have to come out of the tank into the air or else end up looking long and low. Not quite the easiest thing to pull off. I have a 20 long, and it has that sort of problem. Too shallow to really look good. It makes a nice river tank, but that is about it. When I add hills they are so close to the surface it is hard to do anything with them.