I say this is a tough question because different folks will have different opinions--ALL REASONABLE. Everyone needs to decide for themselves. That said, here are my thoughts.
In the under $40 range, I like the Tenacious--very nice fit and finish for a relatively inexpensive knife. I talked with Sal (owner of Spyderco) about the knife when I was writing my book (more below). As I mention in my book, he told me that if you are careful, you can get really good product from china. The Tenacious is an example.
In the $100-$150 range, you have a lot of good options. The PM2 is a nice knife--I own three of them (don't ask). One problem I find is that some of the PM2's have a very sticky compression lock, so I would only buy this knife if I could try it out first or be able to return it.
In the $150-$200 range, my CURRENT favorite is the Zero Tolerance 0770CF. I love carbon fiber--it is very light and very strong. The ZT0770 is assisted, which I do not like, but I deassisted my knife and it works just fine. This is a sturdy knife but is thin and easy to carry at only 3 ounces. It comes in a variety of great steels, such as Elmax, M390 and CPM M4.
In case you are interested, my book is called "A Primer on Folding Knives." I wrote it for both NEW and EXPERIENCED knife users. You can check it out at
www.knifeprofessor.com.