I've carried a SAK since before I was in middle school- as the son of a farmer, it comes with the territory. I started looking at other knives last year, starting with Kershaw and Zero Tolerance. Tried out a few designs, liked a few, but with a few minor exceptions I could never escape the nagging feeling that they just didn't slice as well as my SAK. It wasn't a huge deal, and pocket clips, longer edge retention, and a comfortable grip more than made up for the lack of slicey-ness. I played around with a friend's Delica and Squeak last year and while I was not impressed by the grip (still not a huge Delica fan), I really liked the thin flat-ground blades as they were very reminiscent of the slicing power of a SAK or Opinel and while I still thought they were ugly as sin, I could really appreciate them for their utilitarian design. My favorite knives at the time were Kershaws and ZTs, but with a few minor exceptions, they were all compromises between aesthetics and ergonomics- which is largely (IMO) what Ken Onion does best. However, much as I enjoyed the hobby aspect of knife collecting, my farmer's roots are still prevalent- when I think knife I think tool, and when I want a tool, I want the most functional and ergonomic option available. So I traded for a Manix LW in S110v. To be honest I'm trying to get rid of it now (it's just too wide for easy carrying despite the light weight) but it opened my eyes to the functional design and cutting capabilities of many of Spyderco's products. The handles may not always be the "nicest" materials, but they're textured enough for a proper grip, the pocket clips are always functional, there's jimping in the right places, and they easily open in one hand. Simple construction is good too, especially on the farm, where enough dirt and gunk builds up that I usually have to wash my tools daily.
The short version? When I pick up a Spyderco, I tend to think about how it would perform as a tool. When I pick up a Kershaw or Benchmade, I think about the abstract elements- design, appearance, coloration, etc. Doesn't mean they can't perform similarly, it's just what I've grown used to.