What's your favorite spin off game? Any particular reason?

My favorite is probably either Mystery Dungeon: Explorers of Sky or XD: Gale of Darkness. I'm not even sure how to explain why, maybe it's just been too long. Time, Darkness, and Sky have a really cool storyline and like Red and Blue Rescue Team before them, PMD has great unique gameplay. Compared to Time and Darkness, which are already amazing on their own, Sky only adds more great stuff.