I suppose, given the weather, he'd be on an old BMW SV with driven sidecar or a Ural, however
Here's the real Saint Nicolaus(BIG image)
http://www.show-info.nl/_upload/motorai/docs/sint.jpg
For the scientifically minded:
Santa Claus - Why he doesn't exist - the facts
OK, let's look at this logically. There are about 2 billion children on the world. An average of 3.5 children per household makes 108 million houses in total. We assume that every household has at least 1 good child. Santy has 31 hours to deliver the presents, because of the timezones and the rotation of the earth, at least, if he travels from east to west. This makes 3.48 million houses per hour, or 9.68 houses per second. This means he has, per household, 133 milliseconds to park, jump out of the sleigh, climb through the chimney, put the presents under the christmas tree, climb back through the chimney, start the sleigh and go to the next house. If we assume that all the households are spread over the world, it's approximately 1.3 kilometers from household to household. That makes a total of 140.4 million kilometers that Santy has to drive. That means Santa's sleigh travels with a speed of 1258 kilometers per second, which is 4194 times the speed of sound. A normal reindeer runs about 60 kilometers per hour. Another interesting thing: the weight of the sleigh. If every household would get about 1 kilos of presents, the sleigh has a weight of 108 million kilos, without Santa Claus himself, who isn't that thin either. On land, reindeers can't pull more than 160 kilos. Even if a flying reindeer could pull 10 times that weight, 8 reindeers are useless. We would need 675 thousand of them. The total weight is now 148.5 million kilos which gives enormous friction. 148.5 million kilos with a speed of 1285 kilometers per second. The reindeers will be heated in the same way as a space probe which is going through the atmosphere of the earth. The first two reindeers will absorb about 14.3 billion kilojoules per second. They will probably explode because of that and then the two reindeers behind them will be exposed to the friction. There will be amazingly loud sounds to hear because of this, and in 0.426 seconds the whole reindeer team will have exploded. Meanwhile, Santy is exposed to 17500 times the normal gravity. If he weighs 300 kilos, he will be thrown into the air with a force of 443155 Newton.
Conclusion: If Santy has ever brought presents on Christmas eve, he's probably dead now.
On the other hand.......it's September. It's still three months to go till Christmas/Hanuka/Saturnalia/Whatever. WTF?
AHHHHH MY EYES! MY EYES! 
