Generations gets my vote.
First Contact was the most complicated, sure, but at least our heroes didn't have a choice in the matter.
The Voyage Home used time travel simply as an excuse for our heroes to interact with 20th Century Earth, to very charming and wonderful results. Any time you use time travel as a means to tell a story, and not as the substitute FOR a story, then it's done right. My only gripe about First Contact is that we didn't really see much intergenerational story going on (yes, we had Lily, alcohol, and booze, but that was about it).