20 gauge that turns into a .22?

I've always been a fisherman and me and my grandpa got into a conversation about hunting the other day... I've only been hunting a couple of times... I asked him if when I got a gun, if I could go hunting on his private land. He said that I could, and he also said that I could have one of his guns he used to hunt with. All he has done his life is squirrel hunt... So he mostly has 20 gauges. He said I could have my choice... There is a 20 gauge pump... A 20 gauge double barrel(side by side I think or maybe over and under), a single shot, and another single shot that doubles as a .22 rifle. Which one should I choose? I'm thinking maybe the one that doubles as a .22 rifle. He said you just add this extra barrel attachment and it becomes one... What do you all think? He can't go hunting with me because he's in his 70s and is getting old... He said he would show me the land though so I can memorize it to go by myself. So I will most likely be hunting squirrels... I'd also like to get into rabbit, coon, pheasant, deer, and black bear hunting... (Yes, they have a once a year black bear season for 2 days where I live because it is so overpopulated with black bears...southeastern Kentucky).. Anyways... Which should I choose and why? I know a lot of people might say the pump... But I don't really like the pumps, I like just the simple guns with break action... But list your reasons, etc...