Movies include (in order): The Motion Picture, The Wrath of Kahn, Search for Spock, The Voyage Home, The Final Frontier, The Undiscovered Country. They will be ranked from least to most traumatic in true dramatic fashion.
(6) The Final Frontier - The ship does get taken over, which is bad, but everyone's consenting to the trip by the point they actually pass the Great Barrier which is the most dangerous thing that happens. There's some space adventure shenanigans, but no one from the Enterprise actually dies, and things don't get too crazy.
(5) The Undiscovered Country - There's a lot of stress regarding impending war (or worse - no war!) and Kirk and McCoy both get captured and effectively sentenced to death. That said Kirk and Spock both have a plan (more or less) to get them out of there, and they would certainly have won a war with the Klingons, so they aren't really worried about being in danger themselves - the threat is more that war is generally bad, even if you win. That is the main reason this doesn't get ranked any higher. No one important dies, and everyone's on their A-game here.
(4) The Motion Picture - A perfect example of a disparity between the audience and the characters. While largely a snoozefest for the poor viewers, the characters are freaking out about the potential destruction of Earth the whole time. Spock has just failed at achieving Peak Vulcan through Kohlinar, the Triumverate seems to have split apart hard… they are not working well together and they have to worry about the destruction of Earth on top of that. Nothing is going right for most of this movie, and they're super stressed about it.
(3) The Voyage Home - as fun as this is for the audience, the characters are seriously worried about the imminent destruction of the planet Earth. Not only is the planet on the verge of going kaput, there's some time where it seriously looks to them like Chekov is going to die, and this right after they just got Spock back. Aside from that Spock is… very not right in the head the whole time, so there's the added stress of trying to take care of their recuperating friend. In addition to all this, being in the 20th century was probably very stressful, as they were trying to avoid breaking the timeline while trying to figure out how to navigate a very confusing and difficult culture.
(2) The Search for Spock - McCoy appears to go crazy, and then they learn that he is going to really go crazy if they don't commit treason and mutiny, steal a starship, assault Federation officers and go steal Spock's body from a blockaded planet. They spend the beginning of the movie unaware that Spock coming back to life is an option, so they're worried about losing McCoy in addition to him. Kirk's son dies, the Enterprise explodes and when the movie ends they may have saved Spock and McCoy, but they think they're all going to be sent to mine borite for the rest of time for their crimes. Additionally, they don't even know how many of his memories Spock is even going to recover. My poor space babies. :(
(1) The Wrath of Kahn - Spock dies. That alone takes the win, even ignoring Scotty's nephew dying Chekov being brainwashed into being an accomplice to murder, and the fact that the Enterprise is being run by children who haven't even graduated yet and those children die in astonishing numbers thanks to Kahn crippling the Enterprise. Khan is one step ahead of Kirk for most of the movie, so they're in a constant scramble to keep up, and they only escape thanks to Spock dying horrifically in front of his friends. Ultimate trauma achieved.