RE: Which Gun
I would choose the mossberg 500 that my father gave me. It throws slugs very well, and a bird doesn' t stand a chance at 30 yards.
If only a rifle, I guess a NEF handi-rifle in 30-06...and all the other 20 barrels and calibers you can get for it.
Maybe if I didn' t have my mossberg, that savage rifle/shotgun over and under in 30-30 and 12ga.