In URL rewriting, i am quite confused that should i use underscore **(\_)** OR hyphen **(-)** to replace spaces. According to [**this**](http://haacked.com/archive/2007/03/15/dashes-vs-underscores-in-urls.aspx) and [**this**](http://www.codinghorror.com/blog/2006/04/of-spaces-underscores-and-dashes.html), hyphen should be used.
But [**wikipedia**](http://en.wikipedia.org/) uses underscores like en.wikipedia.org/wiki/Computer\_network\_programming. so which should be used?