Tom,
1)Functional durability - this means the materials and design (good steel and good design)

2)Form - appropriate weight and dimensions for the gauge/use i.e. gamegun weight and balance for gameguns, etc.

3)Quality of manufacture - this means the high quality execution of the design - close tolerances, good machine finishes and fit internally, and good external fit and finish so cherished by many here.

If those three things can be met to my satisfaction, I'd like a boxlock, 16ga ejector, double trigger, straight stock, semi beavertail forend, with no engraving and an option for beautiful wood, weighing between 6 1/4 lbs and 6 1/2 lbs. After that, a 20g, 28g and .410 . I have no use for a 12g if a light 16g is available. But it would be hard to imagine offering a line of guns that excludes the 12g.