Answer:
X-Men: First Class. And it's not close.
Awhile back, I created an animated gif sarcastically illustrating my opinions of all the mutant movies starting with
X-Men and ended before the release of
The New Mutants. It is easy to follow. The higher the Batmobile travels, the higher my opinion of a film. The lower the Batmobile travels, the lower my opinion of that particular movie. I have re-posted it below
As anyone can see, the Batmobile drives up a good size hill for
X2 but climbs the second highest incline to reach
X: FC along the road.
You would be right if the Batmobile appears to drive off a cliff for
X-Men: The Last Stand.