I try to keep blade length on my folders under 3.5". I think the my Emerson A100 is probably a bit over that, but I've found that size to be very usable and it fits most legal requirements. My favorite EDC, is an all titanium Grayman Dua. Not as recognized a name as the others mentioned in this thread, but an outstanding example of knife making. The closed length is about 4" and the blade is a little over 3". It is extremely solid and well made. It also really pushed the limit for what I would spend for a knife, but I have never regretted buying it.