To me it depends on what I want to keep in the tank, and the location that I have available.

I love my 40 gallon hexagon in the corner of my living room. It is tall, and wide enough to fill the space, yet not look like the new collumnar ones (yuck).

I have chosen fish that like different strattas in the tank. ie. guppies at the top, swordtails and neon tetras like the middle, and my clown loaches are bottom dwellers.

This way, everyone has their own "room" to play in, and I've found they get along better provided there are not too many at any one level.

Now my next tank will be taller than a 10, but much longer. This is primarily due to the location available, but winds up working out great because this will be the tank I will breed and raise my swordtails in.
They don't care about height, but they do like a lot of space to swim in.

So, if I were you, I would think, "Tank location, fish, SHOP!!!!"

Good luck and have a blast!!!