How should my urls for articles look?

Hello, Im working on a new project but this time im doing it with an actual website so no wordpress or any kind of cms.

My question is should my urls on my articles look like: /dah_something_does.html or /dah-something-does.html or also I have seen urls like so /?p=1220

So which out of the three would be the best for SEO?

Thanks!

 

use the dashes.

here's my reference hxxp://www.mattcutts.com/blog/dashes-vs-underscores/

 

in my point of view /dah-something-does.html this is the best url structure for you and it is better if you include your keywords to your url

 

I think this format /dah-something-does.html would be better.

 

i would use: dah-something-does.html if i were you, not. ?p=1,