Mobile websites are improving and Google ranks top in the category, according to the Yankee Group, which on Tuesday announced its third annual survey of mobile sites on the internet.

Retail giant Walmart came in second in the analyst firm's US rankings, with three transport sites tying for third. The ranking looked at three key areas: the speed of loading pages, how much data is downloaded when using the site and how often users could access the sites without experiencing failures.

Other factors looked at included the frequency and types of advertisements and how obstructive they were as well as the complexity of accessing information. Sites were marked down if they did not automatically adapt to the user's browser or device.

The awards were split into four categories; a total of 48 transport, retail, technology and national wireless carrier websites were judged. The testers used a variety of devices in New York and San Francisco on AT&T, T-Mobile, Verizon Wireless and Sprint networks.

According to Yankee Group director, Carl Howe, mobile websites are getting better every year with online shopping proving to be the best improvers. He added that apps, such as those found in Apple's App store, were not included in the survey.

"The mobile web is no longer a novelty," he said. "When we started doing this two years ago this was actually pretty was only one year after the original iPhone showed up and as a result there weren't as many mobile web users.

"Nowadays our data shows about 205 million mobile data users in the United States and our forecast predicts that we'll have about...[125 million] smartphones in use in the US by 2014."

For technology sites, Google dominated the space with a score of 81 points. Microsoft's Bing came second with 70 points and AOL came third with 69. Google's use of location-based services, less advertising, and voice-search functionality won the day along with its simple interface and fast response times.