MAC 11 is bomb.com. I regularly use it and have a 1.8 kd with it.
It's only downside is that you NEED extended mags because it empties its magazine like none other. Not like its real life counterpart that fires 32 rounds in 2 seconds. Recoil in game is pretty low, and long distance kills are pretty lulz with it too. Sleight is good too. You could go warlord and use a silencer but I already feel it's a little weak, and I like the handle of the recoil on it without a grip, but it's good with that too.
I hardly ever see people use it.
I wanna use the FAL, but it's just too cumbersome for me.
Also, I adjust my sensitivity for what primary I'm using ie I play at 6 with the MAC and 3 with the commando.