A Blog or website can work with 2 version of www and non-www versionsof the URL. You can enter into your site by typing http://yourdomain.com or http://www.yourdomain.com but both version of domain URL has great impact on the eye of search engine as well as those are technically different URLs. Actually the www prefix is a subdomain of the root yourdomain.com.
You can choose www and non-www versionsof the URL in WordPressbut it doesn’t create any impact on your site traffic but the problem is with Google indexing.
Suppose you are running your WordPress blog by www version (e.g. http://www.yourdomain.com), as a result when Google will index your pages on their search engine then Google will preferred www version. Similarly when you preferred non-www version (e.g. http://yourdomain.com) then Google will index your WordPress pages by non-www version of the URL.
However the problem occur when you frequently switch between www and non-www versions of the URL. As a result search engine will consider the both www and non-www version as separate content link and this is very bad for Search engine optimization. Because Search engine then found lot of duplicate content by same address.
You can easily choose www and non-www versions of the URL on WordPress blog. Just follow the below steps-
Step 1 Go to WordPress Login Page and Sign in to account
Step 2 Go to Dashboard ->Setting
Step 3 Now under General Settings option write your WordPress Address (URL) and Site Address (URL) with www and non-www versions
Step 4 Finally hit the Save Change button from bottom of the screen.
I am personally use non-www versions of the URLs but I don't think so preferred domain has any SEO advantage. But surely one advantage exists on non-www version, most of the users or visitors don't enter whole domain address for visit any site. So often they skip www and enter domain address as http://yourdomain.com so in this case if you are using non-www version then your site will get preferences for visit. If you have any argument about this then feel free to share with us.