I am fairly new to this, but I will add my 2 cents. I have one in a 5 gallon by himself, and another in a ten gallon by himself! I couldn't believe how much richer the color, and more healthy they all looked after being in there awhile.
I have 2 in a ten galon with a divider, and am getting another 10 set up to divide and put two more in. I want to make sure they are free of any ailiments first....
I do have two more in a gallon bowl. They make little bubble nests and seem happy too, though.
The ones in the divided tank look great. They get a lot of excercise having little stand offs in the one corner they can see each other in. The one in the ten looks great too, I might divide it, but hate to, he he always patroling 'his' property.
He is swimming around and flaring as I type this!
( dad gum, just missed another Magic Fish...... those little boogers are hard to catch!)
P.S. SuperSix - LOVE your Bettas!