New domain vs aged subdomain page

When targetting a specific long tail keyword (think Google sniping) is it better to register a new domain with the keyword in it or simply create a new keyword SEO'd page on, say, a PR 2 site?

It seems to me it'd be better to add-on to an existing site (say PR 2) than to create a whole new domain that is brand new and deal with sandboxing, etc.

What do you experts say?

If the domains root is about a completely different topic u may do better with a new domain

Agreed, if the domain is relevant stick with the domain otherwise I'd go for exact match on the domain name if available.

If it's for a product name or keyword that gets too much traffic even a keyword domain can get sandboxed.