Just dont start with the spyderco and benchmade over zt/kershaw!
I think the three companies occupy roughly the same market segment, but they each cater to slightly different tastes. I stay away from Spyderco because the blades are very thin, and I can be ham-handed sometimes. But I've handled a couple, and I agree that fit and finish and ergonomics are darn good for the price.
I like the Benchmade Mini-Grip, along with lots of other people, because it's very hand-friendly. But I'll also agree that the plastic handles make it feel less substantial.
Kershaw does a lot of things right, but it could also be said that a lot of their designs lean toward the "tactical" look, and not everybody is a fan of that.
Each company makes certain choices about the construction and design of their knives to keep them within a chosen price range. Those choices, in turn, influence the purchasing choices of buyers.
Now Zero Tolerance is another matter. Although ZT is a division of Kershaw, the look and feel of their knives are different, and so are the prices. The choices of design and materials make it clear that these are knives meant for doing things you would hesitate to do with other knives. But by the same token, they may not be your best choice to take to dinner with the in-laws.
I don't think it's fair to say one company is "better" than the other two. Like most things, it's a personal choice.