It doesn't matter if you use www or not.
www is a subdomain, no-www is your domain.
Its like comparing ddl.someforum.com to someforum.com. They are quite different.
In google's eyes and probably every other search engine, they're different and www is a sub-domain.
Really, www is outdated but people tend to think it looks nice (although logically, its easier to type the name without it).