O/Us tend to be a bit less expensive than a side by side, or at least used to be.
A lot of people consider an O/U to be easier to hit with, too, because both barrels are on the same sighting plane, as opposed to being on either side of it.
I personally prefer SxS shotguns simply because I'm a traditionalist.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.