RE: Shotguns.....
I shoot a Remington 870 pump w/cantilever slug barrel. The setup works well and accuracy has been better than I expected. Once deer season is over I just put my smoothbore barrel back on and use it for other things. If I didn't have the pump already I would have went with an autoloader such as, Remington 11-87, Browning Gold, or Winchester SX2.
If I was going to have a dedicated deer slug gun that I didn't use for anything else I would try to pick up a Browning A-Bolt slug gun. These were only made for a few years and are tack drivers. You want get anything more accurate without going to a Tar Hunt custom job.
The one good thing about the 870 is that aftermarket barrels are abundant for this model from several suppliers. I got a Hastings economy slug barrel for mine for under $100 bucks used and it's alot more accurate than I expected.