First Contact is the only Next Gen movie that might compete with Generations for top honors, but of course that whole comparison is impossible in the context of Next Gen vs. TOS because fans of the latter will invariably say Generations was the best Next Gen film. This is unfortunate, as it can lead to entirely the wrong conclusion, i.e. that Generations was a fine film and the best of the entire Trek franchise, rather than that the Next Gen movies pretty much collectively sucked balls. Few but avid Next Gen fans will remember Insurrection (for which the cast should be grateful) and what they did to Data in Nemesis is inexcusable. Bad acting aside, even typically thought provoking and complex dialogue like "Assimilate THIS!" is less iconic and memorable than Spock and Kirk in Wrath of Khan and The Voyage Home.

Just for the record:

Star Trek VI: The Undiscovered Country was the best Star Trek film, V was awful, the Insurrection of TOS movies, then probably IV or TMP. THEN Khan (and his meme) and then Search for Spock, which was basically just plot filler and deus ex Genesis after they killed Spock. Which, of course, y'know, may not have ACTUALLY HAPPENED ANYMORE.

If you want to put Next Gen in there, Insurrection is probably some where between III and V, but Nemesis lives up to its name as the worst. First Contact is probably the best Next Gen film, and is at least as good as TMP or IV. I'd probably still put VI first, but not by much. Generations is just sort of... there.... Probably in the territory of better than III and worse than Khan.

And I dare say, there is more than one "right" answer....