My experience is that they're all easily gamed if you want to. As an example, I once spent a year browsing with the Alexa toolbar, and it boosted every one of

My experience is that they're all easily gamed if you want to. As an example, I once spent a year browsing with the Alexa toolbar, and it boosted every one of my sites up into the top 100k just from my own traffic. After ditching the toolbar, they all dropped back down. As to accuracy, Compete isn't even on the right order of magnitude for any of my sites. It's way over for one, way under for another. Just no correlation to reality.