Cost
Regarding gas mileage, the Toyota Avalon beats the Buick LaCrosse.
The Buick LaCrosse doesn't pale in comparison to the Toyota Avalon in terms of gas mileage.
The Buick LaCrosse isn't much less costly than the Toyota Avalon as far as MSRP.
Utility
The Toyota Avalon and the LaCrosse can accommodate the same number of passengers.
Convenience
You'll definitely take the Buick LaCrosse for a fill-up roughly as often as the Toyota Avalon.
Comfort
While the front cabin in the Toyota Avalon offers a bit more head room than the Buick LaCrosse, there really isn't much of a difference.
While the rear of the Toyota Avalon offers a bit more head- and leg-room than the Buick, there really isn't much of a difference.
Dimensions
The Toyota Avalon's tank is approximately the same size as the Buick LaCrosse's, though the Buick LaCrosse's is a bit larger.
The LaCrosse and the Avalon compete for the same parking spaces.
Drivetrain
The Toyota Avalon has a bigger engine than the Buick LaCrosse. Bear in mind that smaller engines are often cheaper to fix, but smaller engines can be stressed more.
Torque equals pickup, and the Toyota Avalon will have picked up and gone by the time the Buick finally gets moving.
Warranty
The basic warranty that comes with the Toyota Avalon isn't quite as generous as the Buick's.