I'm a fan of the 30 gallon tank. It has a 36" by 12.5" footprint, which gives a lot of space for schools to move around. For me, the length and width are much more important than the height of the tank. It might feel huge after a 10 gallon, but it isn't hard to maintain. I'm running one with a small school of Glo-Danios and Khuli Loaches (I'm kind of addicted to loaches).