Best thing to do is to pattern your gun at different yardage and then determine what range your gun will allow you to make an ethical shot on an annimal. For me, I don't shoot at a deer beyond 30 yard w/ a shotgun, 25 yds w/ a bow. This keeps my recovery rate high.

As far as what to buy, it will depend on where you plan to shoot/hunt. My first shotgun was a combo with a slug barrel and a smooth barrel. Because I can use rifles where I hunt, I only use the smooth barrel. For distance shot I use the ML or rifle.