are these different?

is there any difference?

www.domainname.com between domainname.com

what should be used for linkbuilding?

 

You can use any for link building, but SEs consider them as 2 different urls.
So, best is to pick one and stick to it.

 

Different

My suggestion is to pick www.domain.com, and to link only to www.domain.com (I mean internal and external).

So when you get links, link only to www.domain.com

And when you structure your site, link only to
www.domain.com/someting, instead of
domain.com/someting

 

i agree with this

 

another vote for the same,

still your site, should open with our without like

"http://www.yourdomain.com"

 

they are different, I use without WWW. try to redirect www to without www. The set the preferred domain in google webmasters tools

 

hmmmm... i always use with the 'www'

 

Arlene spot on, youre right.

www. is not the same without www.

You basically need to do 2 things:

- 301 Redirection on your server
from www to without www.

301 redirect is the most efficient and Search Engine Friendly method for webpage redirection. It's not that hard to implement and it should preserve your search engine rankings for that particular page. If you have to change file names or move pages around, it's the safest option. The code "301" is interpreted as "moved permanently".

Good guide here

- Webmaster Tools
The preferred domain is the one that you would liked used to index your site's pages (sometimes this is referred to as the canonical domain). Links may point to your site using both the www and non-www versions of the URL (for instance, http://www.example.com and http://example.com). The preferred domain is the version that you want used for your site in the search results.

Here is guide to how to set up your preferred domain on Webmaster Tools

Cheers
Lucio Dias Ribeiro

 

Whichever one you choose, be sure to only build your backlinks to one, and forward the other to the one you choose....Google sees it as duplicate content, and your link building efforts would not show as great results.

 

The member is right you should do redirection and treat your website as it opens in the manner of member shown.
It looks well mannered URL.

 

It depends on you. But me I use www.domain.com

 

thanks I appreciate, this has really helped me..
I guess, for now i will stick with www.domain.ext

 

Personally I rather use non-www than www. I'd suggest you to do the same and just prepare a simple definitive redirection on your server and on webmaster tools.
Simple.
Cheers
Lucio Dias Ribeiro