I have both O/U's and a semi. Both are as different as night and day in their feel and balance. Depending on your duck blind, either might work well or be a PITA, depending on how many in the blind, how close, etc.
A good target gun should weigh about 8 pounds or more for recoil absorption. A good field gun (assuming 12 gauge), should be about 1 pound less for carrying ability in the field.
As to ejectors, no one I shoot with has extractors - they're ALL ejectors. You just put your hand over the barrel when you open the action and they pop into your hand. There are a few models, (can't remember which off the top of my head), that allow you to select ejector or extractor, but that is really a non-issue.
The MOST IMPORTANT factor will be the fit of the gun and the FEEL in YOUR hands. Try to borrow/rent guns of both types and shoot them. See which ones comes closest to a good fit (that way you'll have minimum adjustments to make). Which one swings better for you? Which one does a better job of reducing the felt recoil? Which one is aesthetically more pleasing to you?
Unless someone here actually knows you in person, no one here can tell you exactly what to get. We can give you opinions on what we have found to work well for us as individuals - but that all needs to be taken with a grain of salt.
Personally, I would opt for 2 guns only because you mention waterfowl - a plastic-stocked Beretta/Benelli or similar for the wet conditions that waterfowl typically entails, and something nicer for the clays and upland. Not saying one can't do it all with one. Again , MY preference. And for clays and upland, I like a O/U - two different choke selections, I prefer the balance and swing characteristics of a 30 or 32 inch barrel set.
Good luck in your quest