I love SxS shotguns but did most of my many years of shooting trap with Brownings and Charles Daly O/U guns. If you are seriously interested in an older, more antique shooter, you were given good advice already. I own Parker Bros., A.H. Fox, and L.C. Smith SxS guns, and the quality of those old sweethearts is evident with field usage. It is not too difficult to get production dates by serial # off the internet, and most older gun afficianados belong to an organization or so that caters to collectors of them, offering information, advice, etc. to members. Just remember, these guns are collectors items these days, and can be a little expensive for a decent well-maintained tight-on-face clean shooter. But they were absolutely the cream of the crop in their time. Many revere them quite highly today yet, and rightfully so.
GunBroker can give you an idea of what prices they are commanding on the market today.
If you are interested in newer, less-costly makes and models, the Savage/Fox line is still available, I believe, along with the Browning SxS.