Dashes or Underscores in URLs?Posted by Yzabel
Here’s an article by Matt Cutts (found through ProBlogger) that explain, in a few but informative words, why it’s best to use dashes rather than underscores in your URLs, at least when it comes to Google:
With underscores, Google’s programmer roots are showing. Lots of computer programming languages have stuff like _MAXINT, which may be different than MAXINT. So if you have a url like word1_word2, Google will only return that page if the user searches for word1_word2 (which almost never happens). If you have a url like word1-word2, that page can be returned for the searches word1, word2, and even “word1 word2″.
That’s why I would always choose dashes instead of underscores. To answer a common question, Google doesn’t algorithmically penalize for dashes in the url. Of course I can only speak for Google, not other search engines.
This is probably especially valid for blogs, where permalinks often contain the names ofthe posts themselves. Platforms such as WordPress automatically format such titles with dashes, a good thing indeed regarding Google and perhaps other search engines as well.
To conclude with Darren’s words: For Google, dashes are best.