As big as you can get. Lol no really. As big as you can get. Ok seriously. I like a 40 breeder min size to start. Remember the smaller you go the closer you have to watch your water chemistry. A bigger volume of water is more forgiving. 40breeder gives you lots of options to aquascape. It may, may keep you with that size for a while. The tendency for most people is to start small and wish they had gone bigger. Then they upgrade and need to buy all new equipment for that size tank. Take a trip to a local fish store or even a petco to get a feel for how big the tanks really are if you can
Lol not trying to talk you out of a smaller tank. Lots of people are perfectly happy with them. But I think the majority upgrade in about a year. I upgraded to a 125 about 8-9 months ago but made sure I sized all my equipment for a 180 because I can already see that coming.