My favorite shotgun of all time is the USAS-12. I have not shot mine yet, but it is one heavy and solid piece of gear. I had a Saiga 12 didn't like it at all, it felt cheap and was not reliable like the ak rifle as everyone thinks it is(atleast in my findings). The USAS-12's only fault as of right now is its weight and bulk, but with that it won't kick that much I bet. It looks kinda like a M16 on steriods. It can take 10 round mags or 20 round drums and some sources say it had at one time 12 round mags and 28 round drums. The military versions are selective fire with a 360 rpm rate of fire(mines not).
I do realise that a shotgun like this is really only good for limited roles and you wouldn't wanna be humping all over the place with it. I think the best shotgun to have for practical reasons or if the world went to hell is your basic pump shotgun though. They can eat all that low base crap, work dirty, and don't need lube. For pumps I like my 590, but a 870, 1300, or 37 are good pumps too.