web site traffic statistics and comparison tools

There are various Web site traffic services, none of which are perfect due to incomplete data. They do, however, provide some insight into the traffic levels of decently-trafficked Web sites. The services listed below provide general traffic statistics free of charge.

• statsaholic - Web site traffic comparison graphs side-by-side: shows data from (and links to) comparison graphs provided by Compete and Quantcast (described below)
• Compete - Web site traffic comparison service (along with other paid stats offerings); data obtained from ISPs, panels, toolbars; US data
• Quantcast - Web site visitor data including traffic levels, demographics, comparable/related sites based on visitor behaviour; multiple site traffic comparison charting; ad supported sites usually provide real data versus estimated figures; data obtained from panel (and Web publishers if they provide data); US data
• Google Trends - Web site traffic comparison service (and search term comparison service); provides data by region and over various time periods; includes 'also searched' and 'also visited'; data from search statistics, anonymous Google Analytics data and 'other third party research'
• Alexa - Web site traffic comparison service; data obtained from toolbars and 'other diverse sources'; considered the least accurate of the three services mentioned here