Hyphens vs underscore for URL SEO

[genious]

Which is better for URL optimization hyphens or underscores between words in your URL?
I just came across an article that stated hyphens were better because Google reads words with underscores between them as one word. What are your thoughts?

 

[taniasharma]

As Matt cuts theory Hyphens is more better then underscore. Google don't like special characters like ,"/;_... etc in URL.