Have two 16's, SxS and a pump, Ithica. I love my 16's and would not give one up for a 12 or a 20. Used mostly 12 ga many years ago and there's something about a 12ga. anything you can do with a 16, you can do with a 12! and if you rally feel the need for a magnum then the 20 can step right up to the 16ga. These days I have the two 16's, a 20, two 28's and a 410. Everything but the Ithica is a SxS. The gun I got to mostly is the 28ga. Light weight is great compare one of my 16's to it and the 16's feel like a dump truck. Even the 20 is nowhere near as nice to carry around and recoil of the 28 is well less than anything bigger even though the gun is lighter! If I was to take up duck hunting again I'd grab one of the 16's but I do not really enjoy duck hunting! And they are not my favorite meal! I'm old now and don't enjoy recoil or carrying around heavy thing's, come's with time to all of us sooner or later. I recall shooting a 12ga 3" magnum out of one of my old 12ga guns years ago. Fired one round and threw the rest away. Back then my duck loads, yep hunted them at one time, were 2 3/4" 1 1/4oz #6 shot. Didn't seem to bad back then, today it would let the air out of me. Used to run a bunch of NSTRA and the gun I used was a 12ga SxS with handloads, 1 1/8oz target loads, it was a pussy cat. Now I could have loaded upa 16 to do the same thing And I don't see where there would be a big difference in them. But I think something the 16 has going against it badly is the frame they are made on. Seem's most are made on 12 ga frames and so I've heard in the heyday of the 16 they were made on the 20ga frame. Huge difference in weight!
I think starting a kid out with a 20ga is a mistake. 28ga is a lit lighter and less recoil, 410 even less! I take my 410 out to shoot birds over my dog's training now and then, works fine. And until I got my second 28 I took the 410 as a back up grouse hunting. In fact now and then it was the primary gun. Stat a kid out on a 410 and teach him to use it and if he learn's well, he'll smoke most people. Can't say the same for the 16!
I suspect that the thing I really like about my 16's is that most other people don't have one. When I shot 12's I figured out how to overcome the recoil I didn't like with reloading, simply load it like a 16! Used a 20ga some to, had an 879 Special Field and that was a light gun but had to throw it up and shoot, couldn't track a bird to save my life. Somethng I could notimagine doing with it was shooting a 3" load. Oh no, not in this life time. That gun was as light as my 28's are now, recoil would have killed me. I shot 3/4oz target loads in it also!
I'm not sure what the reason ever was for the 16 in the first place, other than few people other than myself have one. shoot, I don't know one other person today that has one! But with my dislike of recoil and having my 16's and loading for them, I'll never own another 12!