If the Kreighoff has the safety on the tang and not on the side (Greener side safety) I'd buy the Kreighoff, hands down. While I love my various Sauers, the Kreighoff is a much stronger gun and can accept higher pressure insert barrel calibers. For instance a 7X65R drilling could have a full length einstecklauf added to make it a double rifle drilling where that might be an advantage. You could also make it a bock drilling type gun with the shot barrel, the HP rifle barrel, and a 22 hornet or similar in the other shot barrel.
The Sauers aren't sufficiently strong for a second barrel insert like the 7X65R or similar, but they will stand up fine to a 22 hornet or similar round. The Fortuna drilling I have, built on a Merkel/Simson receiver, is stout enough to take the HP round insert. The gun weighs more; that's the trade off.
Fortuna 16 ga 2 3/4" and 7X57R with Greener side safety
Sauer 16 ga 2 3/4" and 6.5X57R with the lighter slimmer Sauer type receiver
Kreighoff Trumpf has stout receiver, top tang rifle cocker/de-cocker, and safety to the left on top next to the cocker