I say go with the shotgun.......I do have to agree though that if you can afford to get an o/u, they make the perfect squirrel rifles. My grandpa has one that my family has been using for a long time, 22lr/.410. The 410 isn't quite the "shotgun" that a 20ga is, but it'll require you take a little bit more time, but it's still better than the .22. (less bbs in the squirrel too)