I think Diego is the more talented of the two and I also would like to see him take on BJ at 155. Diego is right when he said that Joe isn't evolving, and the Joe we saw against BJ is the best we'll probably see.
As for Nate v. Wilson... This should be an exciting match. I see lots of pace mixed with two guys that really know their stuff. I hope to see Nate come out on top, as I believe he'd give Anderson more trouble than Wilson. However, admittedly I don't know THAT much about Wilson. He always seems to slip between the cracks that occupy my attention.
If Diego beats Joe I really want to see him against Sherk. That's be an awesom fight to cardio machines just going at it.