Horner’s STAR TREK II score is on CD a more exciting, interesting score than STAR TREK III if you only have the original album of III.
My view of III changed when I got the expanded edition. Whereas STAR TREK II was a great album in any incarnation, (I think it’s even better expanded, but it’s just the same a bit fleshed out), the OST of III shortchanged the score. In the expanded edition, it becomes a worthy counterpart. I like them about the same, perhaps even with a slight edge for STAR TREK III.