What all are you factoring in to "best"? If its just damage, you cant really say best. You can say highest damage potential.
I forgot to add: The gun that I'm saying is the best delivers the most damage, quickly, with nearly ZERO recoil. Has a large clip, 3.1 second reload and the fire rate is fast enough to do almost THREE TIMES as much damage with two squeezes of the trigger than any other gun I tested.
Again though, I need to test them out in a good area and I need some variations of this gun, including one with no element. I got a guy working on it for me.
XBL GT: Ki11er Six (ones instead of L's and a space between the two words) Various Borderlands 2 glitches: http://www.youtube.com/watch?v=ZgdactVBsYk