I don't see how one really has an advantage over the other. I prefer a SxS but don't see it as having any advantages or disadvantages to any other double barrel.
Go to any sporting clays range, trap field, or skeet field and see how many people are using SxS shotguns. They just aren't in the winners circle at all. I personally like them for grouse and rabbit hunting but when I go target shooting the O/U goes with me. There is no comparison when it comes to hitting clay targets.