[thinkersilver]

Echoing what others I've already said, it's your supervisor and topic should be your main criterion.

Secondly, it depends on what you want to do afterwards whether is a career in academia or industry. If academia see the first point I made.

If it's industry then I'd stress on the networks the institutions afford you. OxBridge in the UK and the usual suspects in the US including Stanford. Remember in industry, the value of the PhD is more in the process rather than the achievement of the title,

Finally look at the time and monetary cost. It takes less time in the UK (3/4 yrs Vs 5/6) and you obtain the same utility from the title as you do from the US equivalent if and only if your optimising for industry placement.

Personally I think the right mix for industry is Undergrad in the US, PhD in the UK; and for academia UK for undergrad and US PhD ( all things being equal).

I hope this helps.