I'Ve had a few of 20 gauges - BSS SxS, Ithaca 200E SxS, Win 101 O/U, Classic Doubles O/U, Win Mod. 12 pump ...all were very satisfactory for grouse & woodcock ... and pheasant & chukar at a couple of club/preserves.
A borrowed Parker Reproductions 28 gauge was just perfect ... alas, not for sale. I've also tried a 28 ga. AyA and an Arietta. Very nice guns indeed.
My current gun is a 28" Union Armera (Grulla)206E 12 ga. box lock with .007" and .017" chokes . It fits very well and balances right on the hinge.
I prefer a SxS field gun for upland hunting. The smaller gauges get the nod for grouse & woodcock ... the 12 for pheasant. I really don't care whether it's
a single or double trigger gun, pistol grip, POW or straight stock, or whether it has a splinter or beavertail forend .... it just has to fit & balance well.
For my purposes, no choke tighter than Light Mod. Light and "target" loads of 7-1/2 or 8 shot @ 1200 fps work just fine, even 9's for woodcock. For pheasants, a little
healthier load of 6's has always worked.