I would choose a TV gun. It wouldn't matter what type or caliber, they're all full auto and never run out of ammo so no need to carry any or extra mags.
I would also get training from one of the actors (excluding Alec Baldwin) where they can shoot blindly into a woods and only hit the desired target plus being able to always hit the bad guys that are shooting at you. You can hit them but they cannot hit you even if they are using machine guns and you only have a pistol.