What is batter ..? Url with under score(_) or url with desh (-)

Yes as above almost all says (-) is better then (_) I'm also agree with them. You can also see hardly few are using (_) inside domin name

 

Yes, so in some cases neither - nor _ will work. You have to keep your url really short.

 

Well Hyphen is better in a permalink structure of a URL.

 

The official Google response is this.....

They USED to respect the traditional computing syntax that stated a hyphen (-) was a gap between things, and an underscore (_) joined things. So a hyphen indicated separate words/phrases, but an underscore indicated joined words/phrases.

BUT in the last few months they've stated they're modifying this so that now underscores (_) are treated as spaces as well.

Their recommendation is to use hyphens if you're starting from scratch, but if you're using underscores at the moment, these are ok too and you should just leave them (because the new URLs will damage your rankings more than the improvement of switching to hyphens)

Does that make sense? It's a little complicated!

Let me know if you want me to explain further