I would avoid TVH primarily because Leonard Rosenman's music doesn't hold a candle to that of Goldsmith, Horner, Eidelman, et al., either on its own terms or as a good fit for the movie. To take one example: The music that begins just as the title card "Music by Leonard Rosenman" appears on screen - all wrong for any imaginable version of Star Trek. As far as I know, Rosenman was a neighbor of Nimoy's, and Nimoy gave him the work as a friend. And indeed Rosenman had done respectable work earlier. But even his great contemporary Henry Mancini's best days were long behind him by the 1980s (both born 1924). Goldsmith (born 1929) was one of the very few of his generation to keep composing memorably for screen.
Allow me to wholeheartedly disagree. :-) In fact, the score to TVH is one of the things I enjoy most about the film.
I think Rosenman's score suits the tone of the film perfectly, and that includes the main theme. The closing cue of the film, when Kirk and company are making their way to the Enterprise
, is beautiful. And, remember, Rosenman's score was only one of two Trek scores to ever be nominated for an Academy Award -- the other being Goldsmith's TMP score.
Further, regarding Rosenman's age and career, he was only 62 at the time he wrote the score for TVH, which hardly qualifies as ready for the grave. John Williams is still composing good quality scores at the age of 82 today. Rosenman's other Oscar nomination came in 1983, when he was 59, and his two Oscar wins came in the 70's when he was in his 50's. It doesn't require youth to write a good score.
Regarding the OP's question -- so as not to totally take this thread off-topic -- I would probably choose TWOK if I had to choose a film to introduce someone to Trek. But, quite honestly, I think the films are the wrong way to introduce one to Trek. Trek (not counting the reboot) has always been, at its heart, a television property. That's where most of the character development happens. If you go into any of the films, including TWOK, without knowing the background of the characters, I think you miss a lot of what makes the movies memorable.