Which is Better Word Separator? Hyphen or Underscore
When Google started as search engine it used to consider hyphens as blank spaces between the words in file names but not the underscores. This trend went on for several years. As Matt Cutts wrote in his blog in August 2005, Google was still considering only hyphens as the word separators. But situation has changed ever since. In mid 2007 Matt Cutts wrote a post that Google was then looking into the matter of considering underscore as word separator. The matter was not still fully resolved then. But Google’s idea & technology continued to evolve. Now they use a better word parsing method that can find words even if you don’t separate them. But still it is better if you separate them so that Google doesn’t parse it into some unwanted words.
Both underscores & dashes can be used as word separators now. I am just giving an example. I searched Google with the words “ppc web spy” screenshot. As you can see from below ppc web spy has been highlighted in the url name even if it is separated by underscores. There is hardly any difference between underscores & hyphens.
But as I have asked the question in the title “Which is Better?” Now from Google’s perspective I can quote Google support:
Consider using punctuation in your URLs. The URL http://www.example.com/green-dress.html is much more useful to us than http://www.example.com/greendress.html. We recommend that you use hyphens (-) instead of underscores (_) in your URLs.
So if you are a stern Google follower you will still follow the long standing word separator. Isn’t it 
By the way, if you don’t know what PPC Web Spy is, I have previously written a post on it. You can check it.
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