According to one of Flamingo's videos, it is confirmed that his favorite is the 1st Pokemon Movie.

Here is proof of Albert's Favorite movie:

This might be outdated due that this video was made in 2021, but it still could possibly be his favorite movie to this very day.

The link to the video can be found here.

Another thing that could be found about his favorite movie is here, where he is wondering what came first, the Pokemon Anime or the Pokemon Video Game

This photo does not show much but it is a little proof.