There is a lot of chitter-chatter about whether or not to include the "www" portion of web addresses. Since sub-domains are becoming increasingly popular and recognizable, the use of the www in domain names has come under a little bit of scrutiny over the past year or so.
There are people that passionately believe that the www is a waste. Why use a www subdomain when you don't have to? After hearing a lot of differing opinions, we decided to take a look at why you would (or wouldn't) use the subdomain www in your urls.
Since we are an SEO company, we looked first at what Google says about it. Matt Cutts described it best when he demonstrated that every instance of a domain is treated differently. In the example, he cited , , , etc. are all treated as separate "pages" and attract links and PageRank individually. Most people tend to link to the www version of an address because it has been that way for so long. Taking this into consideration, you might argue that you want to keep the www in the domain. Matt Cutts addressed this as well, and noted that if you decide to choose not to use the www, then you should do a 301 redirect from the www version () of your domain to the root domain () in order to get credit for links and PageRank that go to the www domain.
Since you can control which version shows up, and which version accumulates links and PageRank, then logically, you can choose which one to use. Be careful to set up your 301 redirects (permanent redirects) and to set the preferred domain in your Google Webmaster Tools though. As long as you pick one and stay with it, everything will work correctly.
Our official stance - we decided this year to keep the www in our domain, and the domains we build. We set up the appropriate measures in Webmaster Tools and with our 301s to cover our bases. This makes it a little less confusing when we build multiple subdomains such as , , or . There is a lot of flexibility around this issue, as long as you make sure to funnel traffic, links, and PageRank to the domain instance that you are using. I would advise against going from one version to the other since the www version of your site and the non-www version will be treated as completely different. And, considering most links do have the www in them, we think it is worthwhile to use the instance of our domain people will be most familiar with.
If you are building a new domain or are thinking about redeveloping your existing one, be sure to think about the impact that a major change will have on your domains authority and rank with the search engines. It takes a lot of effort and link building to get results, so be sure to take the right steps and ensure that your domain's value is protected.