Brafton has reported that Yahoo sites were the top web properties in December 2010 … and November 2010. The latest data from comScore indicates that Yahoo sites are, once again, the most visited web destinations, but now, search giant Google is gaining ground on Yahoo.

In January 2011, Yahoo sites boasted nearly 178.9 million unique visitors. This represents a modest decrease from the end of 2010, when Yahoo sites garnered 181.2 million visitors. With 178.5 million unique visitors, the gap between Google sites and Yahoo sites is closing.

Microsoft sites remained steadily in third place, with nearly 176.8 million unique web visitors, and Facebook remained in third place with 153.0 million unique visitors. Both websites showed general consistency compared to December, when they attracted 177.0 million and 153.9 million unique visitors, respectively.

Meanwhile, Google solidified its lead on Yahoo in terms of ad reach last month. Where Google's ad Network had led Yahoo's Network Plus by a 6.7 percent gap in reach, it now leads by a 7.3 percent margin. Google's ad Network reached 93.1 percent online Americans – 197.1 million unique users – whereas Yahoo's Network Plus reached 85.5 percent of the U.S. internet audience – 180.8 million unique users.

With this in mind, marketers may want to plan ad campaigns on Google. Google recently announced that it is simplifying bidding on the Google Display network to make it easier for marketers to get the most out of their ad campaigns.