1. Star Trek: The Motion Picture
Either this is a great score for a great film, or it's a great score wasted on a mediocre film, depending on your opinion. But it is a great score.
2. Star Trek VI: The Undiscovered Country
A wonderfully dark and evocative score from a relative newcomer. Not only does it fit the film, but it stands on its own.
3. Star Trek: The Wrath of Khan and Star Trek III: The Search for Spock (tie)
These scores are both wonderful contributions to the Trek saga by James Horner, probably two of his most original works (he'd reuse themes and motifs from them again and again throughout his career). It's hard to rank one above the other, and since their so similar thematically (more so than any other two scores for the films), I call it a tie.
4. Star Trek V: The Final Frontier
Definitely a grand score wasted on a mediocre movie. Goldsmith made a career out of that, in retrospect. A wonderful score (wish more of it made it to album) that combines all of Goldsmith's themes, and creates a few new ones, for a wonderfully lush and melodic score.
5. Star Trek: First Contact
Jerry and Joel Goldsmith craft a score that is one one hand as beautiful as the series ever got (Main Title), and on the other, as creepy as the series ever got (Various themes and motifs for the Borg). Sadly, more of it isn't on the album, although it's available from other sources at varying sound quality.
6. Star Trek: Nemesis
A solid score that is better represented on the bootleg than the official release. A shame it's associated with such a rotten film--it might be ranked higher if it didn't have that association, actually. I'll have to listen to it again. It does have wonderful action cues, as well as some softer moments.
7. Star Trek: Insurrection
Goldsmith's weakest score for the series, but it still has its (many) moments, including some interesting themes for the Ba'Ku.
8. Star Trek IV: The Voyage Home
Rosenman reuses plenty of material from previous scores, and unlike Horner's entry, this is not the materials' first appearance. Nevertheless, the chase cues are fun, and the music that plays at the end of the film is perfect.
9. Star Trek (2009)
It works in the context of the film, but is awfully repetitive on what I've heard from the album. I don't actually own this CD yet, so I've yet to hear it many times, but it has not stood up to me on first listen. Rather weak for a Trek score.
10. Star Trek: Generations
This score is too much reminiscent of the "sonic wallpaper" that plagued the series under much of Berman's tenure. There are some nice moments, such as Kirk's Death, Prisoner Exchange, and the Overture, but the action cues are only interesting in that they present music heard on the series with a fuller orchestra.