field shotguns, opinions?

[Bigshooter]

12 gauge will do anything a 20/28 will but not the vica-versa.
Carl

  and the weight difference is only a few ounces.

Couple ounces?  There is a pound difference between most o/u 12ga compared to an o/u 28ga.  Not a big deal when your in a blind hunting waterfoul.  But its a lot nicer when your hunting chukar all day to have a light gun.