The highest number is the one that would give you the most potential return. If you have a big-time domain and can rank pretty easily on competitive keywords, start at the top. If you’re a newer, smaller site and can’t really play with the big guns yet, it might make more sense to start in the middle of the sorted keyword research list – these aren’t the “monster” keywords in your niche, but they’re also less competitive, and therefore easier to rank on. 

For example Amazon as compared to a smaller niche Ecommerce website. Amazon does not need a blog to promote its content, the product landing pages alone do the trick and it does not need to funnel down traffic because of its already existing authority and the fact that thousands and millions of affiliates are promoting and bloggers are already writing about the products that get listed - and also that the reviews on the product pages form some fantastic content.
Of all the tools listed in this article, Moz Link explorer is an old one & quite popular.  If you want to compare backlinks between two or more domains, Open Site Explorer is worth trying. This tool works best when you have a paid account of SEOMOZ though a free version of this tool is good enough to get you started checking the backlinks of your site and the sites of your competitors.
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