Not arguing with Aengus' view, just offering my own.
I started VMK just after Everest month. I have only been able to acquire 1 paw print pin in that time and I am a fairly avid trader. I have several toucans. I THINK, not completely sure, the toucan has been available in pin trading events before. The paw print has not.
Historically, Aengus's timeline is 100% correct, but as someone that was not here when everest pins were out, I just thought I'd share my view from a "rare" perspective. To me, the paw print was 1 of the hardest pins to get when I set out on my quest to get 1 of every pin in the game.
ETA: Toucan was in Fin's Trading event on 5/11/2007. Factor that in however you want. To me, the Paw Print is the pin of the day.