This is my most used weapon, and also my complete favorite.
The MTS-255.
It's an extremely sexy and fun to use gun for me. It also matched the way I use shotguns.
It's an effective middle-grounder for the manual vs semi shotguns. It has enough range to get some decent kills, and it also has semi-auto goodness. I like the sights as well. I also think it's the few good-looking guns when you have gold camo on it.
Has anyone else noticed the gold camos getting less detailed? I think BO1 was the best, very reflective and includes pretty black details. From Bo1->MW3->Bo2->Ghosts, it seems that the gold camos are now more just copied and pasted over the gun. It doesn't have the extra detailing, (the black/gold color scheme from Bo1,) it's just a plain gold-on-everything.