Best over powered weapons

I've noticed that there is pretty much 2 main guns people use in multiplayer. The shot gun and LMG (heavy automatic). Half the time you can 1 shot someone with the shot gun IF you shoot them in the head. Now sometimes if you miss that you have to shoot them least 2-3 times to get the kill. The LMG (heavy weapon in the 3rd slot) can kill you in 5-8shots. I know I said 2 weapons but the automatics (primary gun) some of them are good but most just suck and lack that damage. I suggest getting those guns with the ice or fire symbol because those give bonus damage.