I have been the proud owner of a BG-42 TTKK for about 3 years now. Mine has burgandy micarta with the mosaic pins. This knife has simply been a joy to own and use.
BG-42 will hold an edge longer then ATS-34/154CM. At the time I got my knife, ATS-34 knives were made with 1/8th stock but, the thinnest BG-42 was 5/32nds. This added thickness was a tradeoff in my mind, at the time, between slightly better cutting performance in the kitchen and a slightly stronger knife for use in the field. This is a very subtle tradeoff. I really like the way BG-42 performs and in this knife, is a very good choice.
I would consider D-2 if my primary use was going to be in the field camping or back packing. I would want an edge that has more 'bite' and doesn't polish up so it would perform well on rope and wood.
Today, for the duty my knife sees, Talonite is the obvious choice. I am so pleased with my current knife, I can't justify ordering one in Talonite but, still consider it at least once every six months. If my mother would only appreciate the BG-42 TTKK, problem solved (the first time she put in the dishwasher though would be hard on our relationship so, I wait for a better excuse).
My picks:
remote field use: D-2
weekend "car" camping/easy camping use: BG-42
kitchen duty: Talonite (then BG-42 if Talonite isn't an option)