I accidentally just deleted my post…
Here is is again, with the tiny edit I meant to make when I hit the trashcan instead:
I actually don’t think there is any difference in the actual party itself, to be honest… the desserts are the same but with different theming and you’ll have the same view for the entertainment. It may depend on what your main reason for doing the dessert party is.
We go mainly for the few hours of general MK time before the party starts, and then it’s all holiday events after that, with a ride or two as we pass them on the way to other stuff. I hate sitting around for a long time to get a good spot for the parade and fireworks, so I personally would figure out which of my two parties was likely to have larger crowds (use the search function on the main site, and look for “party crowds” to find the blog posts that predict the crowds for each party date) and do the party at that one, since that would save me fighting the bigger crowd for a good spot.
It takes a chunk of time, though, so if you’re going to the holiday party more for the short lines then you may want to choose the less-crowded party date for your dessert party, so as to optimize your free time. Then you can always watch the fireworks from a less-desirable spot and watch the less-crowded second parade (because you’ll be taking advantage of the even lower evens during the first parade).