Including the www subdomain seems to boil down to two conditions.

 1. **Cookies** - Will setting cookies at `*.example.com` cause me grief (incur more traffic) because the cookies will be sent with every request, regardless of subdomain. In this case I would opt to use the www since it gives me the choice of setting cookies at `*.exmaple.com` if I need it (ex. authenticated user cookie), or `www.example.com` to reduce traffic to my other subdomains.

 2. **Aesthetic** - Do I care a lot about how the domain looks? If I really hate the www but am worried about the cookie traffic, I could alleviate the problem by hosting my static content on a whole new domain such as `static-example.com` which would remain cookie free.