I'd avoid a lightweight 12 gauge due to painful recoil and excessive meat damage.
Try some blackpowder shells. Modest recoil and great patterns, deadly on game. Break open shotgun barrels are a cinch to clean. Newer ones (steel shot compatable) are chrome plated, offering more corrosion resistance. I also made an insert for my NEF 12 gauge to convert it to muzzle loading. That was fun but I enjoy the BP shells more.
I feel 12 gauge meat damage is over exagerated. Take a head shot or let'em get a little further away, same applies to any shot gun.
Agreed, plus if you wanted to bring a few slugs along "just in case" the 20 gauge rifled slugs would do the trick on a black bear.
Or if you come across Mr. piggie.
My daughters 20 gauge NEF is a tack driver with Remington rifled slugs. Also a very nice shooter with shotshells.