BMW 535d. BMW gave the current generation of 5-Series cars a mild refresh for 2014, adding this diesel into the mix for the first time. It combines efficiency with robust power in a package so compelling that there's no reason to buy the gas-powered 535i.
The best part of this BMW 535d is the engine, one it shares with the X5 SUV and a 7-Series sedan. A turbocharged, 3.0-liter in-line six-cylinder engine pumps out 255 horsepower and 413 pound-feet of torque. It's bolted to an eight-speed automatic transmission that routes the power to the car's rear wheels.
The Environmental Protection Agency rates this car's efficiency at 26 m.p.g. in the city, and 38 m.p.g. on the highway, making the car 25 percent less thirsty than its gas-powered twin.
Inside, the 535d wins on refinement. Highlights included a massive panoramic moon roof, a 10.2-inch navigation screen and updated iDrive controller with a new touch pad built into it.
The 535d starts at $57,525, but our tester piled on an additional $8,900 worth of relatively mundane options. But for all that coin, the car still doesn't have a backup camera or parking sensors, which is silly, considering they seem to be standard on everything but tricycles now.
But even with the stress of parking by feel, this is the diesel sedan we'd choose.
Mercedes-Benz E250 BlueTec. After the BMW runs away with the midsize diesel crown, it leaves the Audi A6 TDI and Mercedes-Benz E250 BlueTec fighting for second place. That battle will depend on individual buyer tastes.
The Audi is quieter, more refined and more powerful than the Mercedes. Consider it a BMW-lite: It does everything well, just not as well as the 535d.
Meanwhile, Mercedes aimed for value and efficiency with the E250. Although it scores big on each, it loses some sophistication in the process.
Like BMW, Mercedes refreshed this generation of its midsize car for 2014. E-Class models got the kind of face-lift that replaces the relentless severity of the previous version with a fresh dose of style.
Although its peers still use more powerful six-cylinder engines, Mercedes chose to fight a war on price rather than power. It replaced the older six-cylinder diesel with the smaller four-cylinder.
The EPA rates the Mercedes at 28 m.p.g. in the city and 42 m.p.g. on the highway.
The E250 is now the cheapest model in the E-Class lineup, starting at $52,325. That's a cool $5,000 cheaper than the BMW's base price, though after options are added to each, the gap narrows to $3,000.
But the Mercedes makes a few crucial sacrifices that won't sit well with all luxury buyers. The car is slower than its peers, the engine is louder and less refined, and the cabin isn't as plush as that of the Audi or BMW.
That's not to say the E250 drives like a semi. This Mercedes lives up to its maker's expectations. But don't buy it thinking it will handle like a sports sedan.
Audi A6 TDI. This leaves the Audi A6 TDI. Although it does nothing wrong, it just can't beat the BMW at its own game.
Unlike the other cars we tested, the Audi comes only in all-wheel drive. Although this hurts it a smidgen on fuel economy for our comparison, the A6 is still less efficient than AWD versions of the BMW and Mercedes.
Moving the car is a turbocharged 3.0-liter six-cylinder engine that makes 240 horsepower and 428 pound-feet of torque. It's hooked up to an eight-speed automatic transmission. The EPA rates this combination at 24 m.p.g. in city driving and 38 on the highway.
The Audi's $58,395 base price and $66,795 as-tested price were the highest of the group, but you get what you pay for.
The base price includes the aforementioned Quattro AWD system, navigation, the driver-selectable modes, a moon roof and three-zone climate control. Our Prestige model added such things as adaptive cruise control, pre-collision braking, lane-keeping assist, a 360-degree camera and ventilated seats.