"What humorous RPG have you enjoyed most? Give details."
My experience with humorous RPGs is in a similar category with spies and superheroes, but I have had the pleasure of engaging in one game I would consider to have been exceptionally humorous, and that game is Maid RPG.
What is Maid RPG? Well, It's a celebration of the harem anime culture, where a group of attractive girls (occasionally dudes) coalesces around a main character and showers him (sometimes her) with their love and affection, hoping that today will be the day he chooses one between them all, usually to be his bride.
Such is the affectation behind Maid RPG, except that players constitute the group of love-struck girls, in the form of maids. The GM is called the Master, and it's up to him to create the setting for all the drama to take place in the game. Players attempt to complete tasks and raise his affection levels for them, while occasionally sabotaging their fellow maids and trying to raise their stress levels (essentially hp), in order to take them out of the game for a few scenes.
Maid RPG is the type of game that caters to a certain sect of gamers. Non-anime fans will have very little to enjoy in the setting, in my experience, as a lot of the game relies on a player's ability to act out the various tropes seen in harem anime. My only real criticism for the ruleset is that the introductiory scenario, "Birthday Party," is a bit too open ended and without any real drama to engage the players who need a bit more plot to buy in to the setting.
That said, I'd definitely like to take a crack at running an actual 12 "episode" game of Maid RPG. Perhaps it could get enough steam to get a second season.