I've got an ugly little plakat dragonscale male in my 10 gallon. He's just a greenish blue tint with a tannish colored head. He was nearly dead when I got him, but he's livened up quite a bit. God knows how long he was stuck at the shop, I think his lack of brilliant colors had him at the end of everyone's want list.a plakat male would be best IMO on another note have you considered a group of females? theres some very nice ones about these days
Lucky for him I don't like freakily bright looking fish.
His hobbies include picking on the apistos and rubbing his nose against the back of the tank.
He's pretty awesome.
At the OP; I don't think bettas do bad in large tanks, I think they do bad in -deep- tanks. From what I've seen, they're much more active in larger tank sizes. I think an issue about why they're not given larger tank sizes is for one, the small tank is better myth, and the fact that larger tanks usually have larger fish that are nippy and/or aggressive and territorial that can intimidate or kill bettas