Nowadays www prefix for sites is pointless. I don’t use if it isn’t necessary, because it’s like writing the http:// in the browser location bar to view a site. By default, you use http protocol, so you haven’t to specify it. The same is for www, if a domain is correctly configurated, to be reached also without www, the www prefix is not needed. Another reason is: we are in internet, and a text like domainname.extension is clear this is a site (or maybe not for newbie).
There are two problems I got without www. First is that something doesn’t work, like a Google Map key, which you get for a specific domain, www included. Anyway you can bypass it by setting the link without www as a redirect with www.
The second problem is that search engines differently consider www.sitename.ext from sitename.ext, so if you don’t want to divide up ranking you and who link you should use the same site definition. That’s impossible. Www is so rooted that for Seo is better to include it.
So, I’d like to don’t use it but it isn’t still the time to leave it from links, but you can (nearly always) omit it while typing it in browser.