New ideas to the thread:
Do not get an Ithaca Model 37 for clay shooting. The nice ones are 60-80 years old now. They will last another hundred years if you carry them nicely in the field and put a box of shells through them a year. The same with a Sterlingworth, LC Smith, Wingmaster or Browning BPS. These are status guns in my mind, sort of like showing up at a car show with a 1969 GTO or Shelby at a car show. They are not for daily driving or long road trips. They are not as comfortable as modern shotguns, especially the semi-auto, and are not easily repaired or replaced. My firm opinion is that the most practical all around shotgun is a gas operated semi-automatic 12 gauge in the just about $2,000 category. (Beretta or Fabarms to my mind. My cash went for a Fabarms L4s Hunter. Over time, I came to regret not spending more on the fancy looking one, but that was eased by buying another fancy looking shotgun for impressing my friends with bling.) Ruger is RIGHT OUT. I love Ruger dearly but their shotguns are a disaster. The famous Ruger service does not apply and there are no spare parts.
Fit- this can not be said enough- fit is everything. If spending $1500, you owe it to yourself to find a shop that has someone that can do basic fitting. This is not going to be Bass Pro/Cabelas! How do you find such a place?
Go to your local club, before you buy a gun. You will be considered a wise sportsman instead of a sorry noobie. The sorry noobie shows up with the wrong shotgun that cost a lot of money and now is reluctant to spend even more to make it right. This happens many times every season. Ask the fellas. Plan on spending a few afternoons learning and talking. Find out where their gunsmith is and where they buy guns. Look at the equipment board. These are guns that you can inspect and ask the seller questions, the seller is not likely to vanish once the sale is made, and once a shotgun is running it's a LONG time before it needs service. New guns are finicky sometimes until the kinks are worked out. I am much more confident in a used gun with an inspection, test shoot, and previous owner I know than a new gun.
Pump guns are hard on the shoulder, long of receiver, and take some getting used to to shuck shells for doubles.
A good over and under is much more expensive as the expensive barrels and trigger mechanisms are .. doubled!
Side by sides are even more expensive because top quality ones are now not made in bulk.
Cheap double guns sound great if you're an expert and can do your own repair, tuning, have spare guns for when your cheapy is in the shop, and you like tinkering and fussing. If you just want reliable- it's a roll of the dice. You CAN get a real bargain. You can also get a real klinker.
Semi-autos:
Inertia- hard to beat for a hunting gun. Perhaps trade ease of cleaning for a bit harder recoil. (Duck hunting and rough use specialist.)
Gas- Hard to beat of all-around. MUCH softer shooting. You'll notice it right away.
In both cases, modern recoil pads also create much comfort. You'll feel it.
Fit is important!
Weight-
For a hunting gun, I love my Ithaca model 37 at 6 1/4 pounds. It's a joy to carry. In the excitement of a flushed bird, I don't notice the recoil. A few seasons ago I bought a new L4s because my wife was mocking me for my green, brown, and yellow shoulder. A steady diet of pheasant hunting with only an Ithaca Model 37 had bruised me black and blue. No recoil pad, just a butt plate, as they were made in the 40's. I didn't notice the pain, by the way. It's the gun my dad always shot, and I think of him when carrying it.
My L4s is 6 3/4 pounds. This is one of the lightest modern 12 gauges out there. With the long receiver, the weight is forward. After about 4 hours of walking, my forearm is getting sore, where the gun rests. Because of the quality of workmanship and operation, this would be one of the last guns I would ever part with- it's extraordinarily versatile. The only thing I would not care to do with it is take it in a duck boat and use it as a paddle.
My 20 gauge Syren (same as an Elos over and under, around $3k) is 6 3/4 pounds as well. Because the receiver is so much shorter, you want longer barrels. Even so, the balance point is much closer to the trigger. It feels lighter, because of this balance. Even with a good recoil pad and fit, this 20 gauge kicks harder than my L4s gas operated semi auto. It's immediately noticeable, even when the 20 gauge is launching a quarter ounce less of shot. Keep that in mind!
This is why the guys that shoot clay exclusively have shotguns that weigh up around EIGHT pounds, to soak up recoil.
As I mostly hunt, that would be unpleasant. In my youth, I had a turkey gun that weighed that much. It was like carrying a railroad tie around. I came to hate it! With the excellent barrel and choke on my fabarms, as well as it being ready to mount optics and gas operation and good pad to soak up recoil, I would turkey hunt tomorrow with this gun. We're not even discussing modern turkey loads.
Weight- it's always easier to add some on than to shave some off.
That said, having shot 6 1/4 pound guns, I would NOT care to have any gun in the 5 pound range that was not gas operated and for very special purpose like hunting grouse or partridge where lots and lots of walking was done to shoot midsize birds. Maybe for 28 gauge or .410 bore.
What about the gauge?
12 gauge- "I have a Ford F-150. Say what you want but it does it all and I can always find parts and service. We are legion."
16 Gauge- "I have a reloading press!"
20 Gauge- "This is how I was brought up and I'm a darned good shot. It can do anything a 12 can. Really. Really it can." (Stomps foot petulantly, not mentioning the cost of those shells.)
28 gauge. "Of course I have a reloading press and more cool shotguns in the safe than you can shake a stick at."
.410 "If I am not shooting rabbits or squirrels, I am at the skeet range with one foot in a bucket, meat in my sock, and five labradors because I am just looking for more of a challenge!"