Is there really a difference, aside from how the URL actually looks to using the www subdomain on your website?
No, although visitors are more used to URLs with www and may consider the URL broken or strange without, at least that's my experience with some domain.com projects without www. In terms of seo or ranking there is no difference at all, although you should always use a .htaccess to configure the standard for a domain, so if using no www, do a 301 redirect of the www version, to avoid duplicate content in case people link you with www.
Sometimes I use it, sometimes I don't, depends on what looks better...just remember to always be consistent in using whichever one you choose.
It doesn't matter actually but you should set it in .htaccess to pick one or the other. Search engines do not distinguish between www and non-www and will consider either to be a duplicate of the other if both are indexed.