With the OT it’s difficult to decide. Even though Empire has the most consistent score from start to finish, my favorite cues are in Return and Star Wars. If I’d be forced to choose a singular theme to save (not surprising given some of the threads here) I’d certainly pick the entire “Battle Of Endor II” suite, more specifically the cues pertaining the duel and Vader’s redemption.

In regards to the EU scores:
RoTS - What a score. In my mind I picture a completely different movie.
TPM - The score really picks up steam during the third act. Shame it’s so choppily edited in the film.
TFA - Works great in the film, but as a standalone experience I find it dull.
AoTC - Only the main themes appeal to me.