I would say the CS for both are comparable. Both top notch, I will say without hesitation best in the business. At least they have been for me. And I have used them [more so for Spyderco actually] And have had no issues, if anything just gushes of praise on this front. And even if I did get a warranty problem knife, obviously there is some disappointment/sadness like everyone would be right? But I would not be in despair like you may be with some other companies because I know they back their knives up and have such amazing customer service. It really is more like having to take a car in to get a
free oil change vs getting rear ended. The one thing to note is [not sure if it matters to you], is from what I have seen + my friends experience, KAI's turn around on knives sent in is around the 2 week mark. All my exchanges with Spyderco warranty have been around the 4 week mark [actually the quickest they got a knife back to me was 3 weeks, and I have sen a knife in about 5 times, 2 was to get my knives sharpened before I had a sharpmaker]
Quality wise, I have only started to get into kershaws more budget line ups [RJ1, brawler, hoping for a knockout, and few others], and ZT's since last year. I have played around + borrowed the 350, the 301, and 0400 from a friend. And own the 560 and tilt [thank you Thomas!], and hopefully the last of KAI's triple threat, the 777... for this year at least =]. Their fit and finish is comparable to Spyderco's in most cases in regards to the knives I have had in hand + played around
with so far [again I have a limited bubble of experience with them, being in the 2 yr mark + a total of 10 I think KAI products, VS Spyderco about 5 years + over 30 knives]. One thing to add, is some of the ZT's do seem to have a longer "break in" period to find that sweet spot, although it may have just been my encounters
I could keep going, but just in general they are comparable, 2 sides to a coin in some sense. For me, I have gotten a lot of manuals via the spydie side, and a lot of assisted love from the KAI side, not that KAI doesn't have great manual folders or that they aren't if you take the torsion bar out. They are great [and my friends do carry some as de-assisted manuals]. Its just kind of the main difference in my opinion, and had been more tanks from the ZT side, and less tank like folders on the spydie side. Although the two have been intertwining these areas.
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Bottom line, both have great price + quality, both offer a HUGE range of budget to high end knives, both give the consumers the pleasure of purchasing limited run/sprint run knives that test their prowess and let us consumers feel the luxury that technology allows, both have the best customer service [its like the costco and amazon of the knife world, generally put], both spend time on the forums to help out their customers. Basically, you will not be disappointed.
edit: regarding the fixed blade, not sure about a short fixed blade. But I do know they have quite a few fixed blades on both zt/kershaw
http://www.kershawknives.com/searchresults.php?search_by=knifefeatures&search_value=20&brand=kershaw
http://www.kershawknives.com/searchresults.php?search_by=knifefeatures&search_value=20&brand=zt
Check those out for reference.
edit 2 [+ some re-wording of the same paragraph for better flow- its late

]: Hopefully this helps a little. I noticed your points for a lefty, and your title re: the knockout. But some of your sentences seemed to be aimed in general, so that is how I answered it. A