Had a 16 double for a while. Nice good shooting gun. I did not feel under-gunned, but quite well "balanced" for my birding. I did not shoot migratory birds with it. It worked well for me, but a 20 did as well for what I used it.
I would have preferred a 28 for my upland, I think, but the 16 worked just fine. My 20 bore Ithica SA was a good gun, but seemed to recoil out of proportion to it's ballistics.
The 20 bore SKB was a nice gun, but was poorly regulated, so I dumped it.
The 28 I tried was a Ruger O/U & was quite delightful to shoot birds with.