Utility
Neither the Lancer nor the Mazda MAZDA6 has a marked advantage when it comes to seating capacity.
Dimensions
The Mazda MAZDA6 is tremendously more bulky than the Mitsubishi Lancer.
Your wallet will hurt more every time you fill up the Mazda MAZDA6 than the Mitsubishi Lancer because of its larger tank.
The Mitsubishi Lancer and the MAZDA6 compete for the same parking spaces.
Cost
The destination charge is a standard charge for transporting the vehicle from its point of origin to the dealer. It costs about the same to get the Mitsubishi Lancer to the dealership as the Mazda.
The Mazda MAZDA6 is substantially costlier than the Lancer with respect to MSRP.
Handling
With their similar turning circles, the Mitsubishi Lancer and the Mazda MAZDA6 likely handle almost the same into and out of tight spots.
Drivetrain
The Mitsubishi Lancer's engine is considerably smaller than the Mazda's. Note that a smaller engine usually has to work a little harder; on the flip side, smaller engines typically get better gas mileage.
Torque equals pickup, and the Mazda MAZDA6 will have picked up and gone by the time the Mitsubishi Lancer finally gets moving.
Comfort
While the front cabin in the Mitsubishi Lancer offers a bit more head room than the Mazda MAZDA6, there really isn't much of a difference.
The Mazda provides more head- and leg-room to your passengers than the Mitsubishi Lancer does.
Warranty
The basic warranty that comes with the Mazda MAZDA6 isn't quite as generous as the Mitsubishi Lancer's.