netactr

The supply side of the Web Analytics Data market is dominated by comScore, Nielsen//NetRatings, compete, and hitwise. The first two (comScore and Nielsen//NetRatings) provide the most accurate and stable data sets and are quoted throughout the industry. Compete and hitwise are good info sources for triangulating or researching trends but sometimes have wide swings month to month. The Big Four charge Big Bucks for their data streams, but you can get free but still useful bits from their PR departments: comScore, Nielsen//NetRatings, and hitwise.

For example, the favorite ad format in the first week of January 2008 was Leaderboard (728×90) at 30% of all unique ads tracked by NNR, followed by Medium Rectangle (300×250) at 22%, and Wide Skyskraper (160×600) at 15% (source NNR).

compete has a Site Analytics tool that works well with larger sites and, most importantly, is free. Compare the Unique Visitors trend from compete with the (paid) data from comScore for my favorite blog techcrunch.com. They are close but I will let the TechCrunch folks choose which numbers they want to believe in.

compete Techcrunch UV Trend

comScore Techcrunch UV Trend