Andrew Roberts3 said:"The Fellowship of the Ring" is still absolutely perfect to me. Peter Jackson actually stuck closest to the books here, before he started all those ridiculous cuts and changes you see in "The Two Towers" and "The Return of the King." To be honest, the first two movies in "The Hobbit" trilogy felt pretty lukewarm to me—I definitely need to do a rewatch just to refresh my memory... but that last one actually surprised me in a good way. It was better than I expected, though still not quite enough to take the top spot.
I suspect that, given enough time, RotK might eventually emerge as the favorite in this poll. That said, I can certainly see where you're coming from.
On a slightly different note—what specifically did you find so pleasantly surprising about the third film in "The Hobbit" series? Personally, I found it to be rather disappointing.