I know Im coming off as a fanboy for V, but let me stress that actually Im not
I think out of the original 6, there are two movies that are CLEARLY (to me anyway) in a class of their own....which is VI and II
These are by far the best of the pack, and when it comes to the other four the debate begins with me because while those two are on a different level the other four are almost on the same level, thus why I dont get when people say IV is the greatest original ST movie, and people do say that....makes me roll my eyes
V doesnt even come close to VI and II, none of the others do....and when I look at the other four its HARD for me to actually rank them cause they all have their own problems and their own love/hate moments.
Its a hard choice after the first two but this is how I see it
VI TUC
II TWoK
(noticeable gap)
V TFF (the one movie thats a mixed bag)
IV TVH (for the fun factor, storyline was shit)
III TSFS (Lloyd saved this movie or else it would be last)
TMP (I hate to have to do it but its just HARD to actually say "hey I think Im gonna watch TMP tonight" cause I know after hour one Im gonna be bored out of my mind since it just drags on)

But like you said, its all opinion