I have heard it said that when building the rifle, the O/U is easier to regulate that the SxS. I'm not sure I see any reason why that should be so. In both types the muzzles would have to be moved up, down, or sideways relative to each other.

On the other hand, I suspect an O/U's regulation might be disturbed less by putting a scope on or taking it off. It might handle a change in load better.

Either type is strong enough to do the job if they are made right.

The SxS would be a bit easier and quicker to reload.

For my money the SxS looks far better.