The default MG is the best for non-FF users, although I haven't tried out FF + SR MG, but those seem to be the standard now. The LR MG is no longer of use as the MR MG puts it shame.
I use the Backscratcher - National. Cheeser - Royal MG. Which is the really fast one. You would be suprised at how powerful it is. I certainly was. I use this with the fast shotgun aswell. Then max leg it. Then keg. Biff Baff Boff real good gunner.