My carry knife usually depends on my needs of I know ahead of time.
These are the main 4.
ESEE 3
Kershaw Leek
Benchmade Mini Griptilian
Zero Tolerance 0561
For a fixed blade I love the ESEE. It is a bit bulky if I am carrying it and a pistol. Start feeling like Batman with a utility belt. For right around $100 it is a huge bargain. Carpenters pencil for size reference.
The Kershaw is what I keep in my truck. I usually try to switch out to it when I am pulling into the job. I beat it and don't care. The half serrated blade is good for strapping, rope, cording and the like. I get these for like $20 and for an assisted opener it is a great value.
The Benchmade Mini Griptilian is a great, little knife. I wouldn't carry anything smaller. I tend to not carry it as much as some because of its size. I HIGHLY recommend Benchmade. Great locks and quality overall.
The ZT 0561 is what I carry most. Probably too big for most but it is my favorite. It is also very expensive. I got a deal. For the size it is light because the frame is titanium. I would also recommend ZT due to quality and CS.
If I were buying new today I would be looking at ZT, Benchmade, and Spyderco.