Right, so... Here is where you can post all of the relevant reasons for Santa being whomever you had chosen him to be. Since I went with catgirl, I'll list some things that led me to that choice.
Catgirl santa:
Entry from the roof/A cat burglar
Jingle bells ;p
Milk
Logs make great scratching posts
Cats are known for leaving presents... In the cat litter box. <.<;
They're no stranger to being nocturnal
Loves children
Children love them back... Usually...
They're very familiar with trees
They like lazing about near something warm, like a fire... Not from a TV!
The decorations are really their toys
And that's all that I can think of for now.