That varies based on the time of day.
I'm extremely proud of Vault of the Dragon Kings
. I set out to create a grueling, memorable module with a lot of cool background information on an alternate "creation myth" based on dragonkind that GMs could use to weave into their campaign if they wished. I'm very pleased with the response I've gotten from players who faced the challenges therein.
I also really like how Dungeon Interludes
worked together, creating an overarching storyline that can be seeded into a campaign with a series of one-shots. I've gotten a lot of compliments from GMs who sprinkled these scenarios into their ongoing games and really enjoyed how players responded once they started to see how different plot threads started to work together.
But I probably had the most fun writing Mask of Death
. I'm a big fan of the Gamers movie, so getting access to the Gamers 2 script beforehand to read, and to write a module based on the actual movie was very, very cool. I also think I did a pretty good job of creating an adventure faithful to the Gamers genre/motif/idiom with plenty of humor, but still based around a solid module for players and GM alike.