Category Name In Url

I read so many article about it, but there are a lot of suggestions. So i want to ask it lastly.

For forum, which one is the best for seo ?

1) http://www.vbseo.com/category-name/vbseo-3-6-0-gold-released-48648.html
2) http://www.vbseo.com/category-name/vbseo-3-6-0-gold-released-48648
3) http://www.vbseo.com/category-name/vbseo-3-6-0-gold-released-48648/
4) http://www.vbseo.com/vbseo-3-6-0-gold-released-48648.html
5) http://www.vbseo.com/vbseo-3-6-0-gold-released-48648
6) http://www.vbseo.com/vbseo-3-6-0-gold-released-48648/

I'm not sure "/" is change something or not.

According to majority, if category name contains keywords of the website, it's good way to use it in url but however some of them say "it doesnt matter, number 5,6 is ok, it looks clean in the serps."

In my pc forum, category names are like that /internet/, /pc-game/, /flash-game/, /operating-system/...
So i don't know what i gotta do..

Thanks and Happy New Year

'best' really doesn't exist.

If your categories are niche-specific, I would recommend using them in the url. Ie, if most of your forums are called 'general talk' and things like that, it's useless to include it. But, windows-8-forums/something-about-the-os/ would help the SEs know its about windows 8 if there's no other context that suggests otherwise.

so, 3 from your list.

I prefer trailing slash over any other extension or nothing. It makes logical pagination at /vbseo-3-6-0-gold-released-48648/page2/ or /vbseo-3-6-0-gold-released-48648/page2.html a more logical heirarchy. I prefer no extentions as they simply aren't necessary so i would chose the former in this case.

Thanks Brian,
So my forum's url structure is like that: http://www.vbseo.com/category-name/vbseo-3-6-0-gold-released-48648.html

It's like that since 4 years.. All category-name are not niche-specific. So I don't know what i can do. If i change the category name, threads' url will change, what do you suggest for redirect code ?

And do you suggest that change my url structure to : http://www.vbseo.com/category-name/vbseo-3-6-0-gold-released-48648/

Thanks

I would NEVER suggest changing an established url structure.

What if i want to change the name of non niche-specific category ? Cuz one of my category name is: "Internet General"..
I think its not niche-specific :/

Also can you tell me the way to find niche-specific category name ?

Thanks

I still wouldn't change the urls of an established board.

Url structure must be well defined as per google webmaster as i have read , a user must understand the purpose of your website from your given url.