We ask Danny Sullivan. (I mean, DUH. Who else would you ask?) Danny has a set of graphs showing the trends over the last year from comScore, Hitwise, Nielsen and Compete.
So what are the conclusions? While there’s a relatively huge spread on the percentage, the overall slow upward trend is universal for Google. Ask and AOL don’t show significant differences either.
But Yahoo and Live are a different story. For Yahoo, comScore and Hitwise hold steady but Nielsen and Compete show a dip in the last few months. Live/MSN is almost the opposite.
We may not be able to conclusively decide which service is most accurate, but the comparison helps to illustrate general trends among reporting services. This might raise more questions than it answers, but be sure to check out the full article and pretty graphs over at Search Engine Land!