"The site was very effective in driving excitement and interest and really communicating the brand," said Bonny Brown, director of research and public services at Keynote. "Lexus also did very well. Some of their strengths are site organization, vehicle customization features and vehicle photos. Cadillac did very well in all these areas as well, and that's what put it at No. 1."

For the customer experience study, Keynote ranked the luxury auto sites in more than a dozen categories, including customer satisfaction, customer acquisition and attraction to the brand.

Cadillac, Lexus and Saab topped the Keynote Customer Experience Rankings, which measured site success across the more than 250 metrics, including vehicle search, comparison, customization and quote/pricing functions. The brands examined for the study were Acura, Audi, BMW, Cadillac, Infiniti, Jaguar, Lexus, Lincoln, Mercedes Benz, Saab and Volvo.

More than half, or 58 percent, of all prospective customers visiting the Lexus site said they were likely to test-drive a Lexus after doing so, up 11 percent from the number who said that before using the site, Keynote said. Cadillac, whose brand started in the middle of the pack in terms of auto buyer perceptions, skyrocketed after users visited its site. After using the Cadillac site, 79 percent of auto buyers had a positive perception of the brand, according to Keynote.

Saab had the greatest increase in brand perception after buyers visited its site, the study said. The number of prospective customers who had a positive perception of Saab increased by 32 percent after exposure to the site. Auto buyers described the Saab site as "fun" and "friendly."