Pyro Pete's Bar - Bar Brawl Tier 3 seems to be what people are suggesting. I've gone through that battle 10 times and have 4 picture so far. It's not perfect but there's a lot of Badasses in there that drop pictures. You'll also get a ton of Tokens too.
WARNING though - I've seen my money stolen by Rat Thieves and disappear. I kill them and I see my money fall through the floor!! $200k just gone. I know it's not difficult to make money in this game but to see $200k disappear is heartbreaking in any game :P. I've lost about $400K now because of that glitch so becareful... (I hope it only affects me and not a majority).