[ajquigs]

It's interesting reading the responses.
For me, I guess I care about things that are distractions.
I'm fine with cards that carry evidence of the fact that the original owner was a little kid 50, 70, or 100 years ago. In fact, I kind of like "honest wear" - along with the discount it brings.
So, generally I need centering to be decent and have no creases or wear that detract much from the image - particularly important if it touches the image of the player. Corners can be a bit rounded and the borders can be a little discolored - particularly okay if it's uniform around the card.
Here's a decent sense of my taste in pre-war.