I prefer a Browning or Beretta O/U with 30" barrels. Swings well, heavy enough to absorb the recoil.
I also love the Beretta semi autos and kick myself for selling one of the ones I had. Very smooth, and soft shooting. Lots of good competitive shooters use them.
THat being said, you see more O/Us and after shooting them you'll see why.
But as to what is best? Just shoot what you can get your hands on and not break the bank. I've shot with guys with old, no name pums, O/Us , semis and side by sides. Had some really good shots run 25 straight in skeet with just about any shotgun.
What matters is the smile on your face at the end of the day.