I know some of you may still consider this as good metric, but unfortunately the last time google update their page rank are in, guess what? 6 December 2013. Of course they still update the page rank, but they keep it secret.
Solution: Check backlink quality instead of pagerank. you can use tool such as ahref, or ose, or other backlink checker tools.
2. Alexa Rank.
If you interested to buy website with high alexa rank, well forget about it. Why alexa rank useless at least for seo, because the way alexa rank work. Alexa ranking is counted based on users that installed an Alexa toolbar on their browser. guest how many regular people install alexa toolbar? gues who install alexa toolbar? mainly are webwaster or seo people. moreover it's easy to "cheat" alexa ranking, you can simply send junk traffic on it, and done.
Solution: use your google webmaster and google analytic stat.
3. Number of backlink.
Quality over quantity. It's great if your website got 1million backlink, but if it's from spammy comment, then forget about first page at google.
Solution: get backlink from related / authority website. If your website about cat, try get backlink from other cat's website not some weird rusian website.
searchmetric create great ranking factor chart, take a look here (I can't post link, I'll update once I'm able add it)
Sorry if there are typo or grammar error, English is not my native language.