Hi Mastrogiacomo-
Given equal loadings, the 12 will kick more- but this is not the whole story. A light 20 with mag loads will get your attention, for sure. Light field loads in the 12 are usually pretty easy on the shooter, and of course you can load it "all the way up" with 00 buck/or slugs, if you so desire.
I like short doubles too, and like 4" Model 29 S&W's, I can't imagine not having at least one around. My short double these days is an old Elgin arms 12, bobbed to 19 inches a long time ago.
I've known a couple of guys with Stoeger coach guns over the years, and never heard any complaints. Take care & have fun-