Cost
With respect to fuel economy, the Nissan Altima Hybrid has the G6 beat.
The Pontiac G6 pales in comparison to the Nissan regarding fuel economy.
As far as MSRP, the Pontiac G6 doesn't cost much less than the Nissan Altima Hybrid.
The Nissan Altima Hybrid will save you a lots_of_money at the pump every year compared to the Pontiac G6.
Utility
Neither the Pontiac G6 nor the Nissan Altima Hybrid has a marked advantage as far as seating capacity.
Convenience
You will most definitely have to visit your friendly gas station more often with the Pontiac G6 than with the Nissan Altima Hybrid.
Comfort
Taller drivers will substantially enjoy the extra head room in the Nissan's front cabin compared to the Pontiac G6.
While the rear of the Pontiac G6 provides a bit more head- and leg-room than the Nissan Altima Hybrid, there honestly isn't much of a difference.
Dimensions
Your wallet will hurt more every time you fill up the Nissan than the Pontiac G6 because of its bigger tank.
The G6 and the Nissan Altima Hybrid compete for the same parking spaces.
Performance
Regarding horsepower, the Pontiac G6 packs quite a wallop and will knock the Nissan Altima Hybrid down a few rungs. On the other hand, bear in mind that high horsepower engines often command higher insurance premiums.
Handling
With their similar turning circles, the Pontiac G6 and the Nissan Altima Hybrid most definitely handle approximately the same into and out of tight spots.
Drivetrain
The Pontiac's engine is slightly smaller than the Nissan Altima Hybrid's, but not terribly so.
Torque is roughly equivalent to acceleration, and in this respect, the Nissan Altima Hybrid isn't much more powerful than the Pontiac.
Overview
The Nissan Altima Hybrid and the Pontiac G6 have the same basic warranty.