Handling
With its tighter turning circle, the Pontiac Vibe is most certainly nimbler than the Eclipse, something to consider if you do a lot of city driving; on the other hand, note that a vehicle with a tight turning circle may feel a bit twitchy on the highway.
Drivetrain
The Mitsubishi's engine is considerably more massive than the Vibe's. Remember that more massive engines may use more gas than smaller ones.
The Pontiac Vibe could learn a lesson or two from the Mitsubishi Eclipse regarding pickup.
Torque is the force that lets you accelerate quickly, and in this respect, the Mitsubishi is significantly more powerful than the Pontiac.
Utility
Drivers with frequent child-duty might favor the Pontiac Vibe over the Eclipse.
Convenience
The Pontiac Vibe's fuel tank will need to be replenished more often than the unit in the Mitsubishi Eclipse.
Comfort
Taller drivers will considerably enjoy the extra head room in the Pontiac Vibe's front cabin compared to the Mitsubishi Eclipse.
The ampler interior dimensions of the Pontiac Vibe make it substantially more spacious for your passengers than the Mitsubishi.
Dimensions
The Mitsubishi Eclipse is tremendously heavier than the Pontiac Vibe.
Your wallet will hurt more every time you fill up the Mitsubishi Eclipse than the Pontiac Vibe because of its larger tank.
The Pontiac Vibe and the Mitsubishi Eclipse compete for the same parking spaces.
Cost
There frankly isn't much of a difference in gas mileage here, but if you must know, the Mitsubishi Eclipse is slightly more economical than the Pontiac Vibe.
Regarding MSRP, the Mitsubishi costs significantly more than the Pontiac.
Warranty
The basic warranty that comes with the Vibe isn't quite as generous as the Mitsubishi Eclipse's.