ParaManAR15
Sharpshooter
I don't have 1 go to gun, I try to be proficient with all my guns. If the situation occurs where a random gun is in my presence, I've shot enough variety of guns that I could use it. But for the sake of your thread I would have to say my Bushmaster. It's dialed in, I can shoot on the move, able to shoot left handed, compact, plenty of ammo, and had plenty of training with it.