Both of the green autos have been on the market for almost a year now, but only one will stay on the road.

By Alex Taylor III, senior-editor-at-large

FORTUNE -- Americans love a rivalry, whether it is Dunkin' Donuts vs. Starbucks, or the Yankees vs. the Red Sox. So it is not surprising that the simultaneous launch of the Chevy Volt and the Nissan Leaf late last year built anticipation for a grand face-off. Here, after all, were two highly touted new cars, each using electric propulsion in a different way, that would compete for sales to early adopters while piling up environmental bragging rights. Car guys everywhere are betting on the outcome. So who's ahead? So far Nissan has sold 4,806 units of the all-electric Leaf in the U.S., while GM (GM) has moved only 2,870 Volts, which use batteries assisted by a small gasoline engine. Interesting perhaps, except that such early sales figures are virtually meaningless. The sales winner won't be clear until production ramps up. GM intends to assemble 16,000 Volts in 2011 and 50,000 in 2012. Nissan can currently build 50,000 Leafs annually in Japan. Beginning in 2013, it will have the capacity to build 150,000 more at a new plant in Tennessee.

Enthusiasm for both vehicles is high. Leaf owner David Crane, CEO of Houston energy giant NRG (NRG), which is building an electric car charging infrastructure in Texas, says, "My friends and I love it. It has no compromises that I can see." David Champion, head tester at Consumer Reports, likes the Volt because "it's a car you can live with on an everyday basis." Both have attracted elite buyers. AutoPacific, a California market research firm, found that the average Volt or Leaf buyer has an annual income of $150,000, compared with $100,000 for the typical Toyota (TM) Prius buyer. They aren't looking for basic transportation either; more than half the buyers own at least two other vehicles. "You could say they are using them as dinghies," says AutoPacific founder George Peterson. The two cars are cross-shopped, but not exclusively. Only 56% of Volt buyers with a second choice would pick a Leaf.

What about their success in corporate image building? The $43,000 Volt has won a trunkful of awards and been praised for its elegant engineering. That didn't prevent testers from criticizing its cramped seating, hard-to-use controls, and high price. Nissan gets kudos from environmentalists, but drivers find the Leaf, which sells for $34,500, falls far short of its promised 100-mile cruising range in less than ideal conditions.

Who's ahead today? It's Volt, because the gas engine means it never leaves drivers stranded. But Volt's technology is expensive, and more efficient batteries eventually will make it obsolete. In the long run the Leaf gets the checkered flag. "Pure electric cars are the future, without a doubt," says Edmunds.com senior analyst Jessica Caldwell, "and Leaf is a pure electric car."

This article is from the September 26, 2011 issue of Fortune.