I have never owned one.  Who makes the best?  
Folding, or fixed better?
Law enforcement have anything bad to say about them?

Not very utilitarian IMHO. Fixed. I own a Derespina Model 10 Krambit. Like I said before, not very utilitarian unless you know what you're doing with it.

I love the Desperina 10s! Would love to own one, but it's definitely something you have to train with. I believe in stabbing a mother fucker in the vitals, not trying to de fang him.

I have carried them for years, great knives but not a day to day utilitarian design.  If you understand the best way to apply the knive, the folding designs are the best IMHO.  Top of that list is the Emerson, I have one and it's a great knife.  That said, I don't carry it much; I got a Fox FX-599 and, after sanding down the G-10 scales that were a bit too aggressive, it has become my EDC knife.



So, short version- get a folder, get an Emerson if possible, the Fox 599 is a decent knife as well.

I think for self defense a traditional blade will be more effective unless well versed in how the karambit should be used. As for law enforcement, I think you would have a hard time arguing that it's for any other purpose but self defense. That may or may not fly with them.

I took Steve Tarani's class a couple years back and I really like the karambit for defense.

On the practical side.... You almost need to carry a second knife for the 99.9% of the time utility use of carrying a knife.

I own the 5.11 fixed and folder and an Emerson folder. All solid knives.

I tend to carry an Emerson or Spyderco w/ wave to backup my pistol

100% agree, I carry an Emerson Karambit (mostly folder & sometimes fixed) but I found the need for a second knife too.  I'd definitely look into an Emerson, if you want a fixed blade Karambit Emerson makes one but I also like the Bush Monkey Knives Karambit.