This one was easy for me. Star Trek VI - The Undiscovered Country!!! I would have loved to have seen the further adventures of Captain Sulu as a follow up...
Voted for STII: tWoK mostly because of the phaser buzzsaw effects. The storyline was OK too. Almost voted for ST: TMP instead - I love that one too. Mostly 'cuz of the new Klingon music that was introduced.
I have a hard time getting into the Picard Era movies. They aren't bad, but I enjoy watching the Kirk/Spock/McCoy character dynamic more. Plus Scotty, Uhura, Sulu and Checkov come up with some great one liners! I'll still watch Picard and company, though.
The new Star Trek movie really disappointed me. Beer factories should never be used as Engineering sections! I felt like the writer(s) were being too sloppy and too lazy with the storyline and taking too many liberties with the characters. The special effects didn't save this one for me either.
I would have much rather have seen Enterprise do the movie thing. Or Voyager. Or DS9...