For me it is impossible to boil all of Spyderco down to 5 knives. So instead I put together groups of knives that I think cover many of the bases for Spydie collecting. This does leave a lot of wiggle room for personal preference, while sticking to somewhat specific categories.
Paramilitary 2, it is such an outstanding knife that it easily singles itself out.
Any Seki-City FRN handled knife of your choice, they are all great and are many people's first introduction to Spyderco. That is why they should be in everyone's collection.
A higher-end Taichung made knife be it a Sage, Techno, Domino, or Southard; they are all excellent.
Something large and US made, pick from among the likes of the Manix 2/Manix 2 XL/Military/Police
Something classy, along the lines of the Chaparral, Caly 3/3.5, or Kopa