I suppose that I don't really think of any one knife when I think of Spyderco, although for me, the Military is the flagship Spyder above all others. I would have to say the Military, followed by the Police and lastly the Endura as the Spydies that best represent Spyderco, IMO.
Military--Evolving Spydie that has gone through many changes through the years and considered by many(myself included) to be Spyderco's flagship model.
Police--What can I say, it's a classic....
Endura--Very affordable Spydie for the common individual who doesn't want to hurt his wallet, but still craves great quality craftsmanship in a dependable work knife.