I still haven't seen Episode Yellow, but I would say Onigashima is my favorite so far. Deneb is my favorite Imagin out there and when you make a movie focused on him, I'm going to like it a little more than usual. So, the movie already has points going for it in my book, I did really dislike the Decade stuff as it didn't do...well, anything, so I just like to ignore that and focus on the stuff with Yuu and Deneb that makes it my favorite Den-O movie.
Though, as I've said before, I generally like all the Den-O movies, so they're all good...er, well, except for Episode Red, that movie just sucked.