If there be a dragon associated with Christmas, it follows Saint Nick around and steals anything he hasn't nailed down, then lies on it all year thinking happy thoughts.
It would explain where all those wish-list ponies went.
Honestly, when the MM lists all dragons, metallic or chromatic, as having double standard treasure, I think that says something about the whole draconian avarice thing (oh, and the word 'covetous' has prominent position in the MM paragraph on metallics). Even if he were riding a silver, I'm certain that the silver would nip out just before dawn on Christmas Day, and take all the toys from the naughty kiddies and sit on them for the rest of the year going, "I'm a good dragon! Mweeheehee!"
As such, I imagine that a silver would be most suited to the Man In Red. Habitat matches, general alignment matches, and... hey... it says in the MM that silvers often take the form of 'kindly old men'. I'm not kidding, look it up.
Rides a silver? Maybe he doesn't have to...