Well, FreeBSD has jails and MAC, so I'd reconsider your platform choice
if you say that security is the top priority. China adopted FreeBSD
presumably because of its security benefits. Wether the simplicity
weighs against this or not, is up to the site's peculiarities. In my
case, I choose OpenBSD because of its straightfowardness.
The last string is the tld (top-level domain) and has nothing to do with
the interpeter used by your site's scripts; e.g., ".pl" is supposed to
represent domains hosted for/from Poland, whereas ".com" domains are
usually purchased by _com_panies.
Whatever works out better for you I guess. It's a great
technology, in my opinion, specially when you take in account that it's
33% faster than IPv4.