UK vs US PhDs

Hey everyone I wanted to start a thread about choosing between UK and US PhD programs. As many of us might be stuck between these very fortunate but equally distressing choices, I felt some advice from folks here might prove helpful.

Some of such questions that have crossed my mind so far:
What are some of the major differences that one should consider while making a decision?
Does a three year PhD from UK disadvantage you in the US?
Does one make you better prepared for the job market than the other?
How much weightage should one give to accessibility of archives?
I have been told that US programs typically prepare you more for teaching while in the UK one has to actively seek these opportunities?
Are certain fields more popular in one place over the other? (For example science and war seems to be huge in the US while themes about empire and science seem to be more widely discussed in the UK)

Thanks a ton!

P.S I am a history of sci&tech applicant currently deciding between UPenn(HSS)/Princeton [both funded] and Cambridge (no word on funding yet).

(I have reposted this from a fourm in history section of the gradcafe, to gather opinions from the other side of the pond. Most folks over at gradcafe have suggested picking an US university. Here's a link to that discussion: https://forum.thegradcafe.com/topic/102091-uk-vs-us-phds/)

You really should do your own research to work out what the major differences are in education systems. They are very different mainly in terms of how long it takes, how funding works and what the expectations are. Whether or not you are prepared will depend on which job market you want to enter. Ideally its a good idea to study where you want to work or at least have a good idea of what the expectations will be when you move to where you want to work. You can always go your PhD in one place and move elsewhere for your postdoc(s). If you need archives make sure you have access to them. Yes you are expected to do far more teaching in the US than you are in the UK and opportunities here need to be sought out. The bottom line is to pick the best place for your research.