which one is more reliable - alexa ranking or google pagerank

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I have always been using both meters to find out popularity of a website. On one hand Alexa ranking is completely based in number of visitors looking at a website , staying on it and turning onto its different pages. Google however gives page rank depending on few facts like back links an quality of a web page. Alexa is a relative comparison while Google is absolute marking on a scale of ten. but the truth is that a website having good Alexa ranking has automatically a good page rank. !! One think is that google pagerank is given for each and every URL while Alexa rank is given to domain of the site ( so nothing exists like Alexa rank of your blogger's blog , it will show alexa rank of www.blogger.com instead What do you think about these two meters of quality of a website please share your knowledge too.