Utility
Neither the Forte nor the Mazda MAZDA6 has a marked advantage as far as seating capacity.
Dimensions
The Mazda MAZDA6 is tremendously more bulky than the Kia Forte.
Your wallet will hurt more every time you fill up the Mazda MAZDA6 than the Kia Forte because of its larger tank.
The Kia Forte and the Mazda 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 roughly the same to get the Kia Forte to the dealership as the Mazda MAZDA6.
The Forte is tremendously less pricey than the Mazda MAZDA6 as far as MSRP.
Handling
With their similar turning circles, the Kia Forte and the Mazda MAZDA6 most definitely handle almost the same into and out of tight spots.
Drivetrain
The Mazda MAZDA6's engine is substantially bigger than the Kia Forte's. Keep in mind that more sizeable engines may use more gas than smaller ones.
Torque equals pickup, and the Mazda will have picked up and gone by the time the Kia Forte finally gets moving.
The Kia Forte could learn a lesson or two from the Mazda in terms of pickup.
Comfort
While the front cabin in the Forte offers a bit more head room than the Mazda MAZDA6, there frankly isn't much of a difference.
The ampler interior dimensions of the MAZDA6 make it significantly roomier for your passengers than the Kia.
Warranty
The basic warranty that comes with the Mazda MAZDA6 isn't quite as generous as the Kia Forte's.