I do a bit of traveling and collect an awful lot of currency- http://i.imgur.com/CWkjX.jpg - So I'd also like to chime in on this. I like the US cotton bills as they get better with age. Of course, having crisp bills is nice, but nothing stays that way for ever. My polymer bills maintain creases and it makes them hard to sort. Where as the cotton bills age gracefully.

Check out the AUS 10, see how folded it looks? Now check out the $5 Military Payment certificate from around 1951. Just an observation.