Just like many other things, the tool is only as good as the person using it. You could go out and spend some fat cash on a high dollar gun and still never be very good with it. there is no "Best Gun" IMO and anyone, IMO, that tells you there is, may just be partial to one brand or another. Same thing if you were to ask what is the best bow, or truck or even baseball bat. Bottom line is you need to find something you are comfortable holding and shooting, and then shoot it, shoot it a bunch. Shoot different types of slugs through it also. You will most likely find some kinds work better than others. You mentioned a mossberg 500. That is what I shoot and it is deadly for me. I shot 3 deer last year with it, 2 of them at just over 70 yards and one close to 90. The 2 at 70 were one shot kills each and the one close to 90 got a second slug when I got within 20 feet of her. I bought the gun off a guy at work who said it shot like crap. I spent some time sighting it in with a new slug barrel and got to know what slugs shot the best and I have been hammering deer with it for the last 5 years.