I've had the same domain name for over a year. The previous website I had was just a basic site, not WordPress.
In Google results that site would show the full url 'http://www.domainname.com' which I liked a lot.
I'm in real estate and ALL my marketing materials and business cards have the www before the domain name.
So... when I switched to WordPress (with Godaddy) all the domains being picked up in google are just the domainname.com
Both domains work, but since most people WILL typing in the www (from advertisements), I would like to keep that.