For a general purpose hunting shotgun, I'd suggest a semi-auto. It'll give you 3-5 shots, and will afford you great flexibility for every variety of game. If it was going to be strictly a trap/skeet/upland bird gun, I'd suggest the o/u.
Ditto what Mike said. Since ya just gotta have one, and left skeet/trap/sporting clays listed below actual hunting, have to pick the semi-auto.
With that said, IF pheasant and grouse were the main targets, I'd then choose the O/U, but with dove and waterfowl on the list, semi gets my nodd.
My Bennelli hasn'tmissed a lick in any conditions with any ammo.