To be quite honest, I'm ignorant as to what the differences between "http://example.com" and "http://www.example.com" are.
I typically always use the shorter version, without the "www," just for the sake of the length. But I know (think) that there can be cookie conflicts when users try to access a site when they alternate the version they're using. So on all of my sites I just have "http://www.foo.com/bar" redirected to "http://foo.com/bar". But is there anything to be said about using the "www"?
www is just a subdomain like any other. There's nothing inherently special about it. Back when most of the interaction with the Internet was services other than HTTP, it made sense to have the HTTP traffic use a specific subdomain. Nowadays, the vast majority of domain names exist simply to serve up HTTP traffic, so the distinction is unnecessary. I think it's generally preferred to use the "shorter version" as you call it, and redirect www to the main domain.