The definition of 'good shot' will vary upon the strengths of the weapon type.

Looking at champions in each field as vapodog said those chasing pure accuracy in a hunting gun will usually be in the single barrel camp.

The extremes of target accuracy then goes to bolts and SS.

I would say the best shooter of a double, all else being equal would be he who handled it the fastest above all else.'Quick handling' is the doubles prominent strength.
Any mug can get its 'acceptable' accuracy levels.

The extreme or greatest ability of the greatest SS hunter would be 'picking his shots on game' since you only get one.

However for the 'extreme range shooting' at game the bolt guy with his fastest calibres is more expert in wind drift, and range estimation etc.

Karl.