It seems like most collectors strictly collect only unc examples, or, the highest grade possible. But, I find very little interest in 66PPQ bills, and would much rather prefer a strong XF. Why? UNC bills have no history. They're like remainder bills: they've just sat around in a warehouse or a drawer somewhere and never been used. They're quite uninteresting. When you hold a circulated bill, it means something. It's been through stuff. It lived. I especially like bills with tasteful writing. I have a 1957 $1 silver cert with, "Good luck, Gram" written in old-fashioned cursive. That's really cool. And I like that note a lot better than a crisp, uncirculated bill.