I'm not sure what the designations mean. However, the "best" depends on your intended use of course. For me, sharpest is always the cirterion. The sharpest I ever tried is the 110mm for the RZ. I used it 95% of the time. For interiors and some landscapes, the 50mm ULD (not the Z version) was very good as well. I never owned any of the APO lenses so can't comment about them. It's a fine system camera.