Doesn't matter really, stay with what you are comfortable with. Personally, if I had a chance to own a SxS, I would use it for the field as they are usually a pound lighter than an equivalent O/U but for practice, I would go O/U for skeet. Clay birds fly alot faster and sight/barrel alignment makes a big difference.
I own only one O/U and can't afford a SxS at the moment. It's just me as I won't buy a Turkish or cheap double barrel shotgun. Resale value and there's something about a nice shotgun that screams, 'Tradition!' to me.