TMP: For me the best part is actually just the music and title credits, mainly because of the unique way the music starts with two heavy big drum beats which isn't used in any other rendition of the TMP theme -
Which is ironic since Goldsmith didn't like that version, which is why you never heard it outside of the theatrical and Special Edition tape of the movie, or the soundtrack album. The DE has the album version which Goldsmith always wanted up front.
This not so cut and dried for me, since each Trek film has brought out different feelings upon first viewing (anticipation, reunion, dread, what-have-you). Once we got past the disorienting angles of the fist pass of the Kelvin and all the shaky crap, the George Kirk death scene was the most emotionally moving on a pure filmic level. It would have been moving in ANY film.
This is why I don't consider it for the top spot. It's not "Trek Centric" in a way that would be special on an "omigod it's Star Trek!" level.
BEST OPENINGS:
TFF is the most effective to me because it sets up something mysterious and reverent, while throwing in the chill of a laughing Vulcan. It made little sense to non-Trekkies, but to the rest of us, it was an upending of expectation. Coupled with Jerry Goldsmith's last truly great Trek score, this opening is a total home run.
TMP is my second favorite: 10 years of waiting, wondering, and then seeing Klingons (those scum) in their amazing new ships, with their new foreheads, speaking not-English, and then being obliterated, sets up an epic mystery. I was gripped. For awhile.
GEN: Because it's Kirk doing great stuff, Shatner showing us he still had the chops to play Kirk (which he forgot to do in the last half of the film), and watching the characters react to his (should have been) death.
TSFS: purely emotional, this opening scene sets the tone for the film to follow, a sad journey of sacrifice and love. It stands out as a very dour, but lovely tone poem to the characters and what they mean to each other. It had the largest heart of any of the films and remains my all-time favorite Star Trek movie.
TWOK: A nice, clever way to deflect death anticipation. Well done.
WORST OPENINGS:
TVH: the sheer disappointment of not hearing James Horner's superior theme made this film a real lead weight. Plus, the opening was just a Federation's Eye View of the first minutes of TMP. Blah
INS: What a real "who cares" opening. Data goes nuts and terrorizes white people making bread. Wheeeeee. "What could make Data go nuts?" Well, he's a machine, it's happened enough times before, YAWN. Now if this were PICARD, it would have been a real shocker.
NEITHER HERE NOR THERE:
TUC: Good explosion, but Sulu? Meh. Didn't care.
FC: Yeah, Borg, big zoom out. Props for the shock of the bit coming out of Picard, but the music telegraphed it.
NEM: Annoying "backward" lettering, crappy actors as Romulans, but the effects of the decaying guys was pretty cool. I really don't get a thrill over seeing non regulars in the beginning, and TFF was the only movie to be a real shot in the arm without seeing a single regular.