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 Mercedes-Benz C-Class.
The Mercedes-Benz C-Class won't tax your gas budget substantially more than the BMW will.
The BMW 3 Series won't save you much money at the pump compared to the Mercedes-Benz.
In terms of MSRP, the BMW 3 Series doesn't cost much less than the Mercedes-Benz C-Class.
Utility
Neither the BMW nor the C-Class has a marked advantage when it comes to seating capacity.
Convenience
You most definitely won't have to visit your friendly gas station more often with the 3 Series than with the Mercedes-Benz C-Class, because both offer comparable ranges.
The BMW 3 Series's fuel tank will need to be replenished a bit more often than the unit in the Mercedes-Benz C-Class.
You'll very likely take the Mercedes-Benz C-Class for a fill-up about as often as the BMW 3 Series.
Comfort
Taller drivers will markedly enjoy the extra head room in the C-Class's front cabin compared to the BMW 3 Series.
The BMW 3 Series is not particularly more spacious for your passengers than the Mercedes-Benz C-Class.
Dimensions
The C-Class is a bit more ponderous than the BMW 3 Series.
The BMW's tank is about the same size as the Mercedes-Benz C-Class's, though the Mercedes-Benz C-Class's is a little larger.
The BMW 3 Series and the Mercedes-Benz C-Class compete for the same parking spaces.
Handling
The Mercedes-Benz and the BMW 3 Series have roughly similar tires.
With their similar turning radii, the Mercedes-Benz and the 3 Series most definitely handle roughly the same into and out of tight spots.
Drivetrain
The BMW 3 Series's engine is markedly smaller than the Mercedes-Benz C-Class's. Remember that a smaller engine usually has to work a little harder; on the flip side, smaller engines typically get better gas mileage.
Torque is roughly equivalent to acceleration, and in this respect, the C-Class is quite a bit more powerful than the BMW 3 Series.
Overview
The Mercedes-Benz C-Class and the BMW 3 Series have the same basic after-sale protection.