IMHO, I don't think any tracks in Ultra Blue can be called filler. They're all individual and different, any of them could have been singles. And I love the album and even voted for it in the other thread.
Now however, my vote goes to (miss)understood. It's a lot easier to listen to and quite optimistic too. Plus some of the tracks are just fun, something Utada doesn't have on Ultra Blue. One Night Magic isn't much fun, it's quirky and interesting but never uplifting.
I listened to both albums recently over and over again, and I liked (miss)understood more.
Although nothing can beat the Kairo/This Is Love combo.