Is there any difference in using an underscore vs. a dash in the directory portion of the url?

[RobertFisher]

A friend who is a software developer asked this question regarding the directory portion of the url: Is it better to use dashes or underscores? I know in the domain name Matt Cutts recommends dashes, but what about the directory extension?

[DavidKauzlaric]

Hyphens are always best! Good luck.

[eyepaq]

As far as I know underscores are not seen as separators so that means two words with an underscore between will be tagged as one word.

My personal suggestion is to avoid underscores as much as possible. All separators are good beside underscores.

We work a lot with hyphens and the results are good.

Hope it helps !