SimilarWeb and Compete.com turned out to be the most useful. This wasn’t because their predictions were accurate, but because the correlation between their numbers and ongoing traffic trends were consistent. For instance, while Compete might have shown you had two or even three times the amount of traffic per month as your own analytics, the correlation between traffic spikes and drops would be accurate. These sites are also useful in comparing one site against another (again, due to correlation, not prediction accuracy). When everything is said and done, there is no site out there that can accurately predict your traffic. What should you do about marketing, then? This is where marketing savvy comes in handy -- useful content, clear offers and calls to action, reputation management, and excellent customer service -- combined with the ability to drill down into your own analytics and make informed connections and decision based on accurate information. Using Alexa and other similar sites seems to be largely a waste of time, and in a worst-case scenario, could see you throwing all your marketing money behind an ineffective campaign that won’t benefit your bottom line in the least.