Really I could have voted for any of them (maybe not Tall Tales), but I went with What Is and What Should Never Be because (a) it's got Joey Ramone's cover of What a Wonderful World, (b) it breaks my heart but good, (c) it's a little wincesty at the end, and (d) I think it's the first episode where I thought, This Jensen dude can really act! Like, act his ass off! I never thought he was a bad actor at all, but in this episode he just knocks it out of the park, over the fence, and into the hot dog vendor's tray of tube steaks floating in nasty water.