Well, I certainly think you'd have alot of choices if you want to keep a puffer on it's own in either a 20-gallon, or a 55-gallon tank. I have many different kinds of puffers, and none of mine are so aggressive that I can't put my hand in the tank. I've been bitten several times too, but not so hard as to break the skin, and usually it's been what I think is a curiosity bite -- except for when I've been bitten by my suvattii. Them I have to be careful with because they see your fingers and they think food and shoot up and got you before you know it!
Sorry .... I got away from the topic there ....
My Fang's puffer is interesting to watch, but so is my Abei too. I think maybe you'd be better off looking through the PufferPedia, and making notes of which ones you'd like and then go from there. The list is actually quite long given the choice between a tank of 20 or 55-gallons.
