For me, it was something of a progression. My first Spyderco, a Peter Herbst, convinced me of the value of the Spyderhole, but it was wrong handed and about as ergonomic as a stick. The Native convinced me the midlock was the best lock for me, and that the 50/50 choil was a very desirable feature, but the gimmick grind, partially occluded Spyderhole, and less than totally comfortable handle left room for improvement. The Calypso Jr, came closer to the mark, its only annoyances being the silly beveled spine and the sharp transition between the thumb ramp and the rest of the spine. Then the Stretch came along, perfect ergos, great blade, only the SS/Kraton handle as a downer. CF version cured that, but was still a bit too thin. FRN version fixed that.
Of course, the one that got me hooked the worst was the Kiwi. Perhaps because I was never one for rings, bracelets, chains, or watches, it became my perfect little platform for highly functional jewelry.