The older lens looks essentially new -- not even a mark on the tripod foot.Then it is probably less used and/or more well taken care of. So it must be a better choice.
My 600 II doesn't have a mark on the tripod foot, either. Of course, that's because 5 minutes after first unpacking the lens, I swapped out the Canon foot for the RRS replacement, and packed the Canon foot away in the case.
But still a heavily used lens will show signs of use on other places...