Hmmmmm.... I'd say This One (Crying Like A Child) is my favourite, simply because it's a very typical Utada-esque song.
But then again Apple And Cinnamon is a great song... And Come Back to Me is good as well!

And I really like Poppin', I think it oozes typical Utada charisma! I know people don't like it, but I love it!
I dunno, the whole album has its high, and all the songs are typically great!
Me Muero is also another favourite of mine, I think it's sassy, sexy and very misunderstood, which makes it a great little number.

I guess I should mention Merry Christmas Mr. Lawrence - FYI, seeing as this one seems to be a fan favorite. I'd say the biggest let-down of the album would be... Automatic Pt. II, I was expecting so much from that song, and it was a bit of a let-down... Oh, God, look at me giving a review!

I dunno,I like most of the songs, but This One (Crying Like A Child, Me Muero, Come Back to Me, Poppin' and Apple and Cinnamon are my favourites (obviously I can't have just one!)