I had a hang fire once with a pump action, the action unlocked and partially opened before the powder charge lit off, blowing out the side of the shell and throwing all of the shell's contents out through the ejection port. Fortunately, only my dog was with me, and he was heeled on the other side, but because of that event I'll never shoot another pump action again. Unnecessary risk with zero upsides.
gas operated semi-auto's for the win when it comes to shooting things that are moving. the modern designs are super reliable, recoil is reduced, and they cannot open prematurely. fixed breech guns (O/U, SxS) are fun too. I can't comment on slug guns, except to say that I use an inline muzzleloader instead of a slug gun for deer hunting.