Velocity is a derivative of acceleration.
In a vacuum, both cars would reach the bottom of the hill simultaneously. Remember:
Combining the two equations, the masses cancel out:
We can verify this answer by plugging in some hypothetical values into the kinematic equation:
is the change in distance,
is the initial velocity,
is the time, and
is the acceleration.
Because all environmental and design attributes are identical, let's set the initial velocity to zero, and the distance to the hill's bottom to 2 meters:
Notice how the car's mass did not impact the calculation to determine how long it took each car to reach the hill's bottom.
Both cars would reach the bottom of the hill simultaneously due to friction being ignored.