Multiple TLD or all Sites on one Page?

Hi,

I want to build an site for three different countries: US,UK and Germany.

In general, what's the best approach, seo-wise?

site.com
site.co.uk
site.de

or

us.site.com
uk.site.com
de.site.com
with .de and .co.uk 301 redirecting to the .com domain

or


site.com/us
site.com/uk
site.com/de
with .de and .co.uk 301 redirecting to the .com domain

I'm interested in rankings on google, traffic and the work involved to support the site.

All on one site would be easier to backlink I guess, but would it rank as well in the different coutries as the specific TLDs?

Thanks!

I would go for option 3 and then use GWT to allocate the specific countries to the specific url.