I would disagree somewhat. The original Christmas Ale, as brewed now by Thirsty dog is a completely different beer from the one Great lakes does.
The great lakes one changes year to year as many seasonals do.
I personally think they are both fantastic, though now that the GL one is so popular, all the beer nerds shun it. The thirsty dog beer is much lower in IBU's, higher in alcohol, and way spicier! Its a more outrageous beer but GL's is much more balanced.
mmmmm.... I think ill go to my beer vault and do a side by side comparison....