ArcaMax

Now, it's true that diesel costs more than gas. Well, more than regular unleaded gas. But thumb through the manual; you'll discover the Benz requires premium - and the Acura recommends using it (meaning, if you don't use it, the car's performance and mileage will be less than optimal).

The cost differential between premium unleaded and diesel is much less than it is diesel vs. regular unleaded. Which means the major cost differential is what you pay up front - amortized by what it costs to run the thing down the road.

The Benz CLA250 costs about $1,700 more to buy than the A3 TDI. But it won't take long to recover that in down-the-road fuel savings. And once you hit break even (after about two years, rough-mathing it) you're saving money every time you go for a drive. The math is less favorable vs. the ILX, but you will probably still come out ahead eventually. And if you must have AWD, the ILX gets crossed off the list regardless.

All three of these cars are - sadly - automatic-only. The Benz has a seven speed, the Acura an eight-speed… and the Audi a six-speed ("S-Tronic" automated manual). Normally - if these were all gas burners - the Audi's six-speed would be something of a liability, fuel efficiency-wise, at least. But diesels are low RPM/high-torque engines and so the additional gearing isn't necessary and might actually gimp the car's mileage and performance.

The Audi's transmission has Sport and Normal modes as well as driver-selectable manual control of gear changes (via steering wheel-mounted paddle shifters or by tapping the gear shifter).

ON THE ROAD

With diesels, it's different. What you've got is the reverse of what you'd have with a gas-engined car. Instead of building revs to build speed, the speed is just… there. Be careful with the pedal. It is easy to spin the tires (FWD versions).

Now, the A3 is not as quick - by the stopwatch - as its two main rivals. But the swell of torque and the right-now thrust that goes with it makes the A3 feel quicker than it actually is. Low and mid-range part-throttle response is particularly good. Once you adjust your driving style to make the most of the diesel's power curve, you may find you prefer the diesel's more easygoing nature. It's quiet, too.

As or more quiet, in fact than many current direct-injected gas engines (which is pretty much all of them). Which diesel at idle. Some of them so loudly you'd swear they were diesels. You can thank Uncle for this. Direct injection provides a slight fuel-economy benefit over port fuel injection and because of the pressure to meet the government's ever-upticking fuel economy decrees, you get a gas engine that ticks like a diesel (if it's gas direct-injected). The TDI is also very long-legged.

I've written about this before (see my review of the VW Touareg TDI here). The great distances one can cover in a diesel-powered car vs. something otherwise similar but gas-engined. Despite the technology available today, gas-engined cars get pretty mediocre mileage (example: the gas-engined A3 1.8 TSI tops out at 33 highway). Especially if you hammer them. Not so the diesels. Even running at bring lawyers/guns and money speeds, the A3 TDI never dipped below 38-something MPG while in my hands. I tried, trust me.

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