I think you bring up a good question. I believe it’s predicated on personal preference. Like many who have posted here, I have both O/U and S/S. My Side x Side is an old Fox which is a joy to shoot. I use it for light upland game (quail, Grouse, Dove). I have a browning and rug red label, they have 3in chambers so they work well for Pheasants and partridge. I do think that one shoots best with a shot gun that has been fitted. With a fitted gun both mounting and site picture seem to come together automatically. Either way if you’re going to get one or the other, get a pretty one