what would

[Zebradanio12]

what would be a good next size tank after a 10 gallon.

[Tolley]

50g breeder 36x18x18

awesome size right there. But i suppose big as you can.

[KingFisher]

what would be a good next size tank after a 10 gallon.
It all depends on which fish you would like to keep, how much room you have, what you can afford, etc...
I find it easier to choose which species of fish you would like to keep first, and then get the appropriate size tank for that species. Just remember, when the fish profile says "minimum tank size," it does not mean best tank size, the fish will be happier with more room instead of less.