The first business day of every month is when automakers release sales data for the previous month. Today, we got January’s sales figures, which are an improvement over last January’s.

But the question that we keep hearing is: Which sells better, the 2011 Nissan Leaf or the 2011 Chevrolet Volt?

They’re the first two plug-in electric vehicles sold in the U.S. by major manufacturers in a decade, and now they’ve been on sale for roughly six weeks. The first Leaf was delivered in San Francisco on December 12 (pictured, above), and the first Volt followed three days later in New Jersey (pictured, below).

Thus far (as of yesterday), the Volt is decisively in the lead, with a total of 647 cars delivered through the end of January. That represents 326 in December, plus 321 more last month.

In comparison, only 106 Nissan Leafs have been delivered: 19 in December, and 87 last month.

(For the record, Smart also delivered its very first Smart ForTwo Electric Drive last month as well.)

Don’t go jumping to conclusions about which car will do better in the marketplace, though. Both the Volt and the Leaf are heavily back-ordered, and only modest numbers of each will be built during 2011 as the production line and supply chain ramp up.

Nissan has said it will build 20,000 Leafs for the U.S. market–out of global production of 50,000–this year, and Chevrolet initially committed to 10,000 Volts, all of them for the U.S.

In light of robust demand for Volts, however, General Motors CEO Dan Akerson has said the company is looking at ways to raise production this year, perhaps to 20,000 or more. It also accelerated the pace of Volt rollouts nationwide, so that the range-extended electric car will be available in all 50 states by the end of this year.

It won’t be until 2013, when Nissan quintuples its global Leaf production capacity to 250,000, that true market demand for plug-in cars starts to become apparent. Until then, early adopters and green-minded organizations are likely to snap up every one that hits a showroom floor.

Written by John Voelcker, this article originally appeared on Green Car Reports, one of VentureBeat’s editorial partners.