If I had to get rid of all my knives but 3, right now here are the 3 I would keep.
1. BullDog Regulator (because it is such a neat looking blade and it's big enough for most things)
2. I am torn here, between my S5 and the War Dog. BUT I believe I would give the nudge to the War Dog.
3. No brainer, at least not for me. Mud Puppy.
No real scientific facts to base this upon, but I think that with these three blades I could do about anything.
The knife I regret MOST letting slip through my fingers getting is the first fixed blade knife I ever had. My Dad bought it for me when I was 8 years old. It was a western clone or copy of the Kabar. Many years later I gave it to a relative that was about 10 years younger than me. I should have kept it. He has since lost it.
All my other blades, DF, SOD, MilReg, (S5 I guess), and Swamp Warden I could get rid of. I would regret it, but it wouldn't impact TO much on the ability to have a knife to perform almost any job.
