The Benelli is a great gun. As long as you aren't using low volume breeching loads to crack a door ahead of the ram.
(Pssst, the low volume rounds don't always cycle the action)
The Remington 870, and the Mossy 500 to about the same extent, are like your Chevy 350. Parts for them everywhere, everyone can work on one, there is no mystery part or tool needed and they run rain or shine.
Some of the high price, gas action shotguns (and I have the FN SLP which I love) can not make the same claim in every environment, under every condition.
If your wallet allows you a super duper high end semi auto, they are out there. But if you have a budget, you are going to be hard pressed to find a better platform to experiment with than the 870 or the 500.