I own and shoot both. Back in my trapshooting days, it was nothing but single barrels and/or O/U's. As has been mentioned, the single barrel under the sighting plane is much more preferred. I can't ever remember a double barrel shooter(SXS) at trap with the exception of a few casual hunters who wanted to see how they could do. Got to be a reason for this,right?
Hunting gun is a different story for me. I always have loved the way a good double handles The classic lines and grace are unbeatable in my mind. My favorite go-to uoland gun is a little 28 ga. SXS I picked up a few years ago. I kind of feel it is maybe easier to pick up the muzzle of the gun with your eyes when mounting at game with the SXS due to it's broader profile. Anyhow, that's my $.02 also......