You should add though that it depends on the tank mates and the betta itself. I have a male in a 10G, he was living with 6 neon's, he ended up living with 2 neons before I figured out it was him killing the neons and I moved them to my 55G.bettas make a wonderful community fish, as long as there isnt any other bettas
And as a point to it depending on the betta, the tank I moved the 2 neons into has a large angel. Anything you read will tell you not to put neons with angels as they will eat them, these neons are small, and have been fine living in there for a couple months now. I realize that might one day change, but it comes back to it depends on the attitude of the fish, not neccessarily its perceived level of aggresion.