You should read HydroGuy's quintessential thread on WDW vets visiting DLR for the first time:
http://www.disboards.com/showthread.php?t=1162599
If I had to choose one of those dates, I'd probably pick the 22nd, but just be forewarned that all of DLR is likely to be swamped that week. So definitely plan on going early and making judicious use of fastpass. With just one day, I would focus on just
Disneyland and leave Disney's California Adventure for a future visit after all the construction is finished.
I emphatically agree! Kate0305, Skip the 27th entirely, especially because you will only have one day to play and you will not be able to get the most out of the trip on a crazy day like the 27th. The last two years, my friends and I stayed at DLR on the weekend right before Christmas, and it was crowded throughout the Resort, but still tolerable. It didn't scare us away. It was manageable. Also, if Santa is important to you to see in this visit, he will not be around on the 27th. He only stays at DLR through the 25th and then he heads back to the North Pole.
Just in terms of crowds alone, while it will be crowded on the 22nd, it will be so much
more crowded on the 27th. That week between Christmas and New Year's is notorious for being hideously packed. I suppose many people who get holiday gift money or who get tickets or Annual Passes for their presents flock to the park in droves as soon as Christmas ends, to see the holiday decorations. This past holiday season, the number of AP holders alone hiked up enormously and the crowds increased right along with them. The bad economy compelled many people to forego vacations in more distant locations and stay closer to home - so DLR was the place to be! So, yes, avoid the 27th at all costs.
Normally, I am an advocate of doing two parks in one day just as a general 'highlight tour,' with the understanding that you will not be able to see everything in one day at both parks - but you can see a lot. For example, my friends and I just did a one-day trip last month and we did most of what we would have wanted to do, but not everything. Another day or two would have been better. Other people would have felt cheated or like they didn't get to do enough, so it really depends on what you need from your DLR experience. I would say, for the purposes of escaping DL when it gets to be a little too congested, head over to DCA where the crowds are lighter during those extra-hectic times in DL. If Monsters Inc., Toy Story (the greatest ride), Soarin', California Screamin', and drawing pictures of DIsney characters at the Animation Academy, etc., are important to you, you will want to be in DCA. If a Princess character meal is important, head to DCA to meet with Ariel and her friends.
Otherwise, just in terms of experiencing as much of the holiday magic that DLR has to offer in one busy, crowded day, stick with DL. DL lends itself to the overall holiday vibe much better than DCA does, I think, so if you really want the best taste of Disney holiday magic in a very short period of time, stay in DL. That is where you will find HMH and IASWH, as well as the Reindeer Round-UP, etc.