Utility
Neither the Audi TT nor the Porsche has a marked advantage as far as seating capacity.
Performance
As far as horsepower, the Porsche Boxster packs quite a wallop and will knock the TT down a few rungs. On the other hand, remember that high horsepower engines often command higher insurance premiums.
With that kind of horsepower, the Boxster is a true sports car.
Dimensions
The TT is tremendously heavier than the Boxster.
The Audi TT's tank is almost the same size as the Porsche's, though the Boxster's is somewhat bigger.
The Audi TT and the Porsche Boxster 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. The Audi is substantially cheaper to get to the dealership than the Porsche Boxster.
When it comes to MSRP, the Audi costs significantly less than the Porsche Boxster.
Handling
With their similar turning radii, the TT and the Porsche Boxster definitely handle almost the same into and out of tight spots.
Drivetrain
The Porsche Boxster has a more massive engine than the Audi TT. Note that smaller engines typically get better gas mileage, but smaller engines can be stressed more.
Torque is roughly equivalent to acceleration, and in this respect, the Porsche Boxster isn't much more powerful than the Audi TT.
Comfort
While the front cabin in the Porsche offers a bit more head room than the Audi TT, there honestly isn't much of a difference.
Warranty
The Porsche Boxster and the Audi have the same basic warranty.