Utility
The Mazda CX-9 will most certainly prove more practical than the Acura RDX for those of you with frequent child-cargo.
Towing is considerably more the Mazda's forte than it is the Acura RDX's.
Dimensions
The Mazda is substantially heavier than the RDX.
The RDX's tank is approximately the same size as the Mazda CX-9's, though the Mazda CX-9's is a bit bigger.
The RDX and the CX-9 compete for the same parking spaces.
The Acura RDX's shorter wheelbase may produce a less-settled highway ride but a sprier feel in daily traffic than the Mazda CX-9.
Convenience
The Acura RDX's fuel tank will need to be replenished slightly more often than the unit in the Mazda CX-9.
Cost
The destination charge is a standard charge for transporting the vehicle from its point of origin to the dealer. It costs roughly the same to get the Mazda CX-9 to the dealership as the Acura RDX.
There honestly isn't much of a difference in gas mileage here, but if you must know, the Acura RDX is slightly more economical than the Mazda CX-9.
With respect to gas mileage, the RDX is a tad better than the Mazda CX-9, but not by much.
With respect to MSRP, the Mazda doesn't cost much less than the Acura RDX.
Handling
With their comparable turning circles, the Mazda CX-9 and the Acura RDX most certainly handle about the same into and out of tight spots.
Drivetrain
The Mazda CX-9 has a more sizeable engine than the Acura RDX. Remember that smaller engines are often cheaper to fix, but smaller engines can be stressed more.
Comfort
While the front cabin in the CX-9 offers a bit more head room than the Acura RDX, there really isn't much of a difference.
The Mazda CX-9 offers more head- and leg-room to your passengers than the Acura does.
Warranty
The basic after-sale protection that comes with the Mazda CX-9 isn't quite as generous as the Acura RDX's.