It is a bit based on the child. My general sense would be AK as well. The environment with the animals, shows, etc. is more stimulating for many children. I think everyone's reasons are well founded.
With that, Epcot also has some elements. The fountains, LwtL, the Seas, etc. can be great (as long as there isn't extreme fear of the dark). And, there are more boat-oriented attractions (indoor and outdoor) at Epcot if that's something your little one may enjoy. Epcot also offers the various entertainers in the countries. (AK has this too. But, Epcot probably offers a little more.)
One other consideration is the heat and being outside. Both parks are pretty large. AK, by design, has fewer indoor opportunities. October is a bit of a gamble weather-wise. If it looks like it may be pretty hot, and your little one is sensitive to that, I may vote Epcot - since you can duck into a theater-based attraction, pavilion, etc. with air conditioning pretty easily from most areas of the park.
Enjoy!!