Welcome to the Q&A Forum

In my opinion this would depend on whether or not your going after this as your primary keyword.  I co-own a site that sells custom t-shirts.  The phrase "custom t-shirts" has always driven the most volume and conversion so we optimize our homepage for it.  If your website is a camera shop and you are launching into iPhone repair or something like that I would be more inclined to link it down to the subpage.  So in my opinion if this is one of the top 2 or 3 keywords you are targeting I would go root domain.  If it is something less than that I would break it down to the subdomain where you can add better supporting content.