Both venues offer some unforgettable character experiences. We've done a lot of both. You say you are going in Dec. Will that be early Dec. or close to Christmas? We were there the week after Thanksgiving in 2002 and had awesome meet & greet opportunities with little wait. In AK, one of the designated meet & greet areas is Camp Minnie-Mickey. We met Donald & Daisy, Mickey & Minnie dressed in Christmas attire, as well as "Santa" Goofy. There was NO line!!! My kids had unlimited time with these characters! We got great pics for our Christmas cards! My son was 15 months old at the time & adored all characters. My DH took him into the Judge's tent at Toon Town while I took DD on Goofy's Barnstormer. At first he thought they were closed, as no one was around. But then he saw Mickey inside. My DS played with Mickey for about 10-15 minutes. It was great. We also happened upon Lilo and Stitch at the Animation Studio area at MGM -- we were 2nd in line. Baloo pushed my DD around in her stroller at AK in the Harambe area. Those are a few examples. At Epcot, a great place to meet characters is the Characters on Holiday bus. There's a separate thread going about that right now too. I would think that if it's a crowded time of year, though, the lines to meet characters would get very long, and the characters only appear for a set length of time.
As for character meals, does your DD like the princesses? If so, both the Princess Storybook Breakfast in Norway at Epcot and Cinderella's Royal Table in the MK have family style service. They bring large platters/skillets of food to your table for everyone to share. It's all you can eat, so they will refill anything you want. That's a great way to see characters without having to leave your table for a buffet. I haven't been, but I believe the character dinner at Liberty Tree Tavern in MK is like that also. My kids love the character meals, but they hardly eat at them, because they're so excited.
Sorry this is so long, but I hope I've helped!