I voted for Doppelgangland. I actually thought it was miles funnier than most of the other humor-oriented episodes...a lot of them wound up being more cheesy or stupid than funny. Even though, like everyone else here, I enjoyed Something Blue and Pangs, I thought a lot of Pangs was a bit stupid and the only truly funny parts of Something Blue were the Buffy/Spike/Giles moments, which only took up a small portion of the episode (plus, I hated Mopey Willow in that episode. I much prefer when Willow lets out her sadness by going evil and flaying people.)
If Doppelgangland wasn't an option, I probably would've gone with Storyteller. The beginning of that episode was absolutely hilarious. I also thought Band Candy was really funny (why isn't it on the list?), but it definitely wasn't the absolute funniest.
Oh, and does anyone else think Tabula Rasa is really overrated? I thought it was kind of funny, but I didn't exactly out of my chair laughing.