I would have to say that there is no debate on my favorite December Monthly Collectable.
It is the December 2003 Nitmares Scarf: Why- multiple reasons... Mainly I joined Gaia in 2003 (on another account before it got hacked) and fell in love with it when it was first reviled. Though it is not multipurpose like the new Monthly Collectibles, the sheer charming practicality yet wicked appeal drew me to it. I was hooked and set on getting one, though that desire never became actuality due to lack of funds. It is still a goal of mine to attain one of these items, though it still alludes me.
I adore the scarf for other reasoning as well. How the scarf appears to be demonic wings thrills me to the core... I know- it just a virtual item for an online site, but still- It is simply spectacular.
I have almost always based my Avatar around the Nitemare Scarf- so for the day I get it it'll be complete.