My favorite is a red label 28g (I've had 20 and 12 both as well but both were heavy and clubby to me) but they are no longer made and hard to get at a reasonable price.
I have hunted upland game from a young age as that is what my father was into the most.
He trained and field trialed "bird dogs" when I was young. We mostly had English setters and pointers for the most part.
All that time until now I have tried many shotguns for upland and waterfowl . I also shoot sporting Clay's as well.
Currently I fave a Fabarms axis , Benelli super sport 12g , sport 20g , M2 12g , CZ sharptail sxs target 12g , cz bobwhite 28g , cz allterain premier 20g , ugartechea 12g , fabarm sxs 12g lion imported by H&K , 870 wing masters from 410 to 12g , winchester model 12 both 16g and 12g and a few others. Not trying to brag as I grew up poor and have been blessed in my career so to over compensate for not having much growing up. I have had brownings and berretta (sporting guns and not really good for chasing birds)along the way as well . I just mention this to say that if I was only gonna get 1 shotgun I would look at the CZ all terrains (sxs or o/u) and I would get a 20g. For the $ I think they bring lots of value , low maintenance and little worry about the conditions they may be exposed to.