Even though I think that Dec. 20th is a cool day, I voted for March Fourth. There's not much gaming around Dec. 20th. I want to celebrate on a day that I would have people around to appreciate me.
March is named March, of course, because it's the month that the Romans would literally "march forth" in their annual campaigns.
In addition, March 4th isn't near any other holiday and it doesn't come near Origins or GenCon, which I consider a good thing (July and August already get plenty of attention from gamers).
I'm not against 3/4. Actually, this whole thing feels kinda silly since 95% of the time I am the DM. Deciding on a date to celebrate myself..... heheh
August feels like a better time to me. No real reason. Maybe the second friday of every August or something easy to remember like 8/8. Either way, it's all good.
Well, I initially voted for 12/20 (I figured you would already be in the whole shopping/celebrating mood), but I've changed my mind and like 3/4 now... I just like saying March Fourth!