It's very complicated for me to choose for one main reason; I haven't had the chance to see a 1968 in real.
However, based on the pictures I have seen, the 1968 model has a major drawback. I don't like the "fake" patina. I considered several times bying a Longine Legend Diver re-edition (BTW, yours is superbe). I tried it 3 to 4 times and this prevented me from bying it.
In my view, it is either an old watch with its own history and patina or this is a new one. For example, I didn't dare to by a vintage Omega SM300, there are to many fakes (BTW, yours is superbe bis). I bought a "new old" watch from a trusted watchmaker with new case, SL dial and hands, only the 565 caliber is from the 60'. Honestly, I happy with it as it is, and would never like to apply a fake patina. It's like pretending being something else that it really is.
In your magnificent quatuor I would be unable to decide between the 1965 reedition and the original 1968 for first place. then the 1968 reedition and last the AMVOX titanium.
Your watch collection is trully magnificent, many thanks for sharing this with us!
Sébastien