Skeet in it's original form of "Shooting 'round the Clock" was originally devised by a group of New England grouse hunters to sharpen up their upland skills. When a neighbour moved too close to their original set-up, the circular field was divided in half to a semi circle and another trap house was added. I'll bet most of them in the early days were SxS shooters. I've managed a good many straight rounds with pumps, semi-autos, O/U's and SxS's. For competition, there is little doubt from the statistics that today, the O/U has the edge, particularly those fitted with sub-gauge tubes. In the 60's and 70's the auto-loaders seemed to have the edge. There were a good number of Model 21 Skeet guns around in the 40's and 50's and Skeet was very popular with the Model 12/42 set in previous times.
As Claybuster has referred to earlier, the gun that handles and balances well, is heavy enough not to beat you up and fits to the point that the gun actually shoots were you look is the one to use. I'd be remiss in saying that most shooters would be surprised to work with a professional gun-fitter in patterning their gun only to find that their guns really do not fit them particularly well ... despite them being able to shoot somewhat O.K. with them.
For most North American shooters, a well made SxS field gun is a little bit of a trial in getting used to ... especially with a straight (and usually longer) stock, higher comb, straight grip, double triggers and lighter weight. But once acclimatized, they are very efficient in the uplands. For grouse, woodcock, pheasant & the like, I'll reach for my SxS every time. The high buck
O/U, target semi's and the old faithful pump for waterfowl stay in the closet.