I wasn't going to answer but in the first 40 responses no one had said it so I have to. Even numbered Star Treks don't suck! Wrath of Khan was sooooo much more entertaining than Star Trek the Motion Picture. Personally Star Trek: The Undiscovered Country is my favorite of the original cast movies though.
Of the Next Generation cast movies my favorite is Star Trek: First Contact. I still think of it as Star Trek: Your Future's End because I saw an early trailer at I-CON that called it that I think.
OK, geeking out over.