I own several of both the old Blackjack Trailguide and the newer Ken Warner version. Both are Mike Stewart products, or at least the first run of Ken's knives were actually made by Mike. The handle on the newer version is significantly larger in diameter than the older Blackjack Knives version. You will also find the newer handle on some Bark River prototypes.
As has been posted, the older knives are A2 and the newer ones are made of 52100. A2 seems to get a little sharper and hold an edge better than the 52100 version, but the difference is minimal. I too like the old handle size better, but if you have larger hands the new one may be more suitable to your tastes. Both are excellent knives suited for a variety of chores.