Gee lawman,
That's really subjective. So much so that you're going to get a gazillion combinations of answers from people.
But if you're just wondering what some of us think. In no particular order:
1. Benchmade Axis 710 in 154CM; M-2 is too fussy for an EDC for me anyway. (little over $100).
2. Spyderco Police Stainless Steel (approx $80 on E-Bay)
3. Microtech SOCOM Elite (under $150)
I own 1. and 2. but don't own a Microtech SOCOM but want one really badly. All three are large, 4 inch blades which are legal in most areas (Canada has no blade limit), still easy to carry, and good for self-defense IMO. They all have general type blades (eg not hawkbill) so they are versatile. Since you want it as a general purpose knife as well, you might want to avoid hawkbill knives although someone is bound to suggest the Spyderco Civilian.
Another bonus is that all three have handles that may come in handy for police work. The Benchmade has exposed steel liners under the G-10 scales, the Spydie has stainless handles, and Microtech has aluminum handles. Keep this in mind in case you need to use the handle butt to break through a window, use it to restrain an unruly culprit, etc. Purely synthetic handles (Zytel, pure G-10, carbon fiber) may lack the mass, or impact to shatter glass easily.
The Spyderco Police, and Microtech have a particularly pronounced point for the butt of the handle so the impact will be concentrated if you should use it to break a window.
The Spyderco Police is a lockback, and some people have trouble closing them with one hand (although I don't have such a problem). You might want to keep that in mind too if that's an issue.
Just my personal taste.
. $79
