Love my 870 cantilever. I put a Boyd's thumbhole stock on it and it does the trick. That said, if I were to buy a dedicated slug gun today, I'd be looking at the H&R USH. You also asked about 12 or 20ga. My 870 is a 12 and my son's is exactly like it, though in 20. Either one is just fine. With today's sabots, I'd probably go with the 20ga.
