Utility
The Saab 9-3's more massive trunk will accommodate more massive objects than the BMW 3 Series.
Neither the 3 Series nor the Saab has a marked advantage regarding seating capacity.
Dimensions
The BMW is markedly heavier than the Saab 9-3.
The BMW 3 Series's tank is approximately the same size as the Saab 9-3's, though the 9-3's is slightly more capacious.
The 3 Series and the Saab 9-3 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 BMW 3 Series to the dealership as the Saab 9-3.
In terms of MSRP, the Saab 9-3 doesn't cost much less than the BMW 3 Series.
Handling
The 9-3 has substantially bigger tires than the 3 Series. Remember that wider tires could improve handling, while smaller tires may improve gas mileage.
With its tighter turning circle, the Saab is doubtless nimbler than the BMW 3 Series, something to consider if you do a lot of city driving; however, note that a vehicle with a tight turning circle may feel a bit twitchy on the highway.
Drivetrain
The Saab 9-3 and the BMW 3 Series have similar-sized engines, with a slight advantage to the BMW 3 Series.
Torque equals pickup, and the Saab will have picked up and gone by the time the BMW 3 Series finally gets moving.
The BMW 3 Series could learn a lesson or two from the Saab 9-3 with respect to pickup.
Comfort
While the front cabin in the 9-3 offers a bit more head room than the BMW 3 Series, there really isn't much of a difference.
The BMW 3 Series is not particularly roomier for your passengers than the Saab 9-3.
Overview
The 9-3 and the BMW have the same basic after-sale protection.