Car shoppers today are spoiled for choice when it comes to fuel-efficient vehicles. When else in history have we had the choice between gasoline, diesel, biofuel, natural gas, hybrid, plug-in hybrid and full battery electric vehicles?

When it comes to actually putting fuel in your tank, many turn to hybrids and diesels to get the most miles to every gallon. But which is best?

Road & Track thinks it can answer. And if you have a Prius, look away now--because it isn't the hybrid.

The magazine lined Toyota's flagship against the Mercedes-Benz E250 Bluetec--a midsize luxury sedan with a 2.1-liter, four-cylinder turbodiesel under the hood.

It's entirely different from the Prius in shape, size, performance and even brand ethos--nobody specifically chooses a Benz to save gas, but saving gas is the Prius's raison d'être.

Testing the fuel economy of two dissimilar cars always risks favoring one over the other based on the driving route chosen.

The Prius, for example, is better in city driving--where the Atkinson-cycle gasoline engine spends much of its time off. Diesels like the E250 tend to return better results on the highway--often beating their EPA ratings.

MORE: 2014 Mercedes-Benz E250 Bluetec: First Drive

To mitigate this, Road & Track picked a circular route around the bay area, with minimal hills, a mix of city, highway and rural routes, and a rule that both cars should keep up with traffic the entire time.

Over 410 miles, each car returned nearly identical economy. In reality, the Benz used a little less diesel, but the margin was so small the difference was within a reasonable margin of error. Each car managed around 43 mpg.

Perhaps predictably though, the Mercedes was given the nod.

2013 Toyota Prius

2013 Toyota Prius

While economy was similar, it proved the more comfortable, effortless way to make progress. At highway speeds it barely broke 2,000 rpm in seventh gear, and made light work of climbs that saw the Prius screaming.

The testers were also impressed with its economy given how few concessions it makes to be an economical vehicle--it's a large, heavy sedan with a diesel engine, rather than an all-out eco car.

It also has by far the longer cruising range: Even after 410 miles, the trip computer showed 534 miles remaining.

MORE: Diesel Hybrids: Why They Don't Make As Much Sense As You Think

There are, however, two elephants in the room--not mentioned in the test.

One is price. Starting at $51,400, the E250 Bluetec may be the cheapest E-Class, but it's also $27,200 more expensive than the Prius. Putting that another way, you could buy two Prius for the price of one E250 Bluetec.

The other is the price of diesel. In California, average gas and diesel prices are currently similar--around $4 a gallon. Across the U.S. though, gasoline remains under $3.60 a gallon on average, while diesel hovers close to $4.

That would make the cost of the trip a little more expensive in the Mercedes than it would in the Prius.

Flaws aside, the trip does highlight interesting differences between hybrid and diesel vehicles.

And while few Prius customers will spend double to get the Mercedes, it's clear that E-Class buyers could save huge amounts of fuel by opting for the diesel--as well as saving on purchase price.


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