What are the 14g cube dimensions? 15″ x 15.5″ x 14″? What would you be keeping in it?
A 20g tall is 24″ x 12″ x 16″. Both are fairly tall tanks for a smaller footprint. Take the footprint only. You lose 9" in length and gain 3.5" in width front to back. When i'm dealing with smaller tanks, I look at the footprint. But also what type of fish i'm keeping. For ex I use tall tanks to grow out my angels. But for most fish, they will use the horizontal space, so a 15 x 15" tank is like 2 x 5.5g tanks side by side for width. So I would stock fish that are good for 10 gallons in the 14g cube.
The biggest problem with tall column style tanks for me is they don't offer a ton of surface gas exchange. So I must keep an airstone or sponge filter to circulate water from low to high and also hopefully help with o2 levels at the bottom for say lower strata fish. Also it limits how many fish that use horizontal space you can keep. At the same time, it offers more room for 2 different strata fish.
But when you really think about it, there's not much difference between a 20g tall and 14g cube really. I mean I would stock similar fish anyway. Purely my 2 cents and probably more thought than you want lol.