Utility
The Vibe and the Altima can accommodate the same number of passengers.
The Pontiac Vibe outpulls the Nissan Altima by a massive margin.
Dimensions
The Nissan Altima is tremendously more bulky than the Pontiac Vibe.
Your wallet will hurt more every time you fill up the Nissan Altima than the Pontiac because of its bigger tank.
The Pontiac Vibe and the Nissan Altima compete for the same parking spaces.
The Pontiac's shorter wheelbase may produce a less-settled highway ride but a more agile feel in daily traffic than the Nissan Altima.
Convenience
The Pontiac Vibe's fuel tank will need to be replenished more often than the unit in the Altima.
Cost
Regarding gas mileage, the Nissan bests the Pontiac.
The Pontiac Vibe requires a lot of gas compared to the Nissan Altima.
Regarding MSRP, the Nissan Altima costs roughly as much as the Pontiac Vibe (though the Pontiac Vibe is a little cheaper).
Handling
With their similar turning radii, the Pontiac Vibe and the Nissan Altima quite certainly handle about the same into and out of tight spots.
Drivetrain
The Pontiac's engine is significantly smaller than the Nissan Altima's. Note that a smaller engine usually has to work a little harder; on the other hand, smaller engines are often cheaper to fix.
The Pontiac Vibe could learn a lesson or two from the Nissan Altima when it comes to pickup.
Torque is the force that lets you accelerate quickly, and in this respect, the Nissan is substantially more powerful than the Pontiac Vibe.
Comfort
While the front cabin in the Nissan Altima offers a bit more head room than the Pontiac Vibe, there frankly isn't much of a difference.
The Pontiac Vibe provides more head- and leg-room to your passengers than the Nissan Altima does.
Warranty
The Nissan Altima and the Pontiac Vibe have the same basic warranty.