I would have to suggest getting a 10-gallon. It's pretty small and would have room for several small fish, and could accomodate a heater, filter, and all the stuff that I would see as basically essential. I had one betta in my 10-gallon and he was happy as a clam. I thought about getting a 2.5 or 5 gallon for my betta initially, and I am so glad I decided to get the 10. When I upgraded to a 29, my 10 became a fry tank/hospital tank, depending on whether I have fry. Like others have said, the somewhat larger tank would give you much more freedom as to the types of fish you could have and really wouldn't require much more work to maintain.