RE: 00 buckshot or a slug
I would bet that most of the votes for slugs have never killed a deer with buckshot. Using a modified choke and under 40 yards, buckshot would be my choice. I use 3" magnum 00 buckshot regularly and have never lost a deer or hog. A couple of years ago, I bought a Patternmaster choke specifically for shooting buckshot and am not sure that it is any better than the flush mount modified that I had been using. I have killed deer out to almost 50 yards using a modified choke, and I have NEVER had to blood trail a deer that I have shot with buckshot. I have killed around 12-15 deer and numerous hogswith buckshot, andnot one has ever taken a step after being hit.
I used to have a rifled barrel for my Benelliwhich shot slugs very well, but I have tried and tried to find a rifled slug that I could get to pattern out of my smooth bore barrel. I have trieddifferent brands and have never been successful getting under a 6" group at 50 yards (which is not acceptable to me).
Good luck with your choice of ammo.