I have a MK1, MK3, MK4, and MK4CF. The Dauntless series is probably one of my favorite for an actual "user". The design is simple, feels good in hand, and works well with bare hands or wearing gloves. I personally like the choil on it, and find it quite useful at times.
MK1: Very nice, but notably heavier than the MK3/4. Good option if you like Ti, and don't mind watching it get scratched up.
MK3: My personal favorite. Flat grind, stiff clip, stonewash, and smooth bushings make for a durable and easily re-buildable knife.
MK4: Lightest and nicest feeling in hand. Definitely the most refined version (especially in the carbon fiber option). Not a fan of the hollow grind when compared to the flat grind on previous versions. Clip is much more flexible, and the hardware uses smaller Torx heads. Bead blasted lock side shows a lot more wear than the stonewashing on MK1 & MK3.
Any of them make a very nice knife in hand, and in use. At least that's my two cents. Let me know if anyone has any other questions.....