Just choose one version and be consistent in your promotion. You may want to setup the redirect in your.htaccess file so regardless which version user use it will get redirected to the version that you choose.
I prefer without the pointless www, but do use www sometimes. I don't really give a toss about sticking to one or the other though. TLD = Top-level Domain, a.k.a com, net, org Not "www.domain.com"
I agree with sharpseo. Its better to stick with www. . Although they don't have any significant affect on seo efforts buts better to stick with www.
I agree for www if you ask me. As for subdomains, I've used to have hundreds of subdomains and I've used NON-WWW version for subdomains (it was sort of more natural for me) and it went perfect for me (personally). Cheers!