Utility
The Toyota Highlander is a better choice than the Mercury Mariner as far as hauling capacity, especially if you often need to carry a lot of equipment or big dogs.
Drivers with frequent kid-duty might favor the Highlander over the Mariner.
Dimensions
Your wallet will hurt more every time you fill up the Highlander than the Mercury Mariner because of its more capacious tank.
The Mercury Mariner and the Toyota Highlander compete for the same parking spaces.
Convenience
The Mariner's fuel tank will need to be replenished more often than the unit in the Toyota Highlander.
Cost
The destination charge is a standard charge for transporting the vehicle from its point of origin to the dealer. It costs roughly the same to get the Highlander to the dealership as the Mercury Mariner.
The Toyota Highlander won't tax your gasoline budget considerably more than the Mariner will.
The Mariner doesn't pale in comparison to the Toyota Highlander with respect to fuel economy.
Regarding MSRP, the Toyota Highlander costs markedly more than the Mercury Mariner.
Handling
The Mercury Mariner and the Toyota Highlander have approximately comparable tires.
With their similar turning circles, the Mercury Mariner and the Toyota Highlander quite certainly handle about the same into and out of tight spots.
Drivetrain
The Toyota Highlander's engine isn't much bigger than the Mercury Mariner's.
Torque is the force that lets you accelerate quickly, and in this respect, the Toyota Highlander is considerably more powerful than the Mercury Mariner.
Comfort
While the front cabin in the Mercury Mariner offers a bit more head room than the Toyota Highlander, there really isn't much of a difference.
While the rear of the Toyota Highlander provides a bit more head- and leg-room than the Mercury, there really isn't much of a difference.
Overview
The Mercury Mariner and the Highlander have the same basic after-sale protection.