Suitability of top UK graduate programs, compared to US ones
I'm not sure about master's degrees, but there are a few important differences between US and UK doctorates.

Duration. UK doctorates can be (and most often are) as short as 3 years. There are now 4-year degrees (the so-called 1+3 degrees), which combine master's degree and doctorates much like the US programmes, but normal 3-year doctorates are still the norm. US doctorates take at least 5 years to complete, and you can often exit with a master's degree. One of the downsides of the shorter doctorates in the UK is that the number of papers you publish during your doctorate will be typically less than the number of publications of someone who had 5 to 8 years to complete their doctorate.

Funding: Unlike undergraduate and master's degrees, which have been turned into a business, where universities are all too happy to accept international applicants who pay exorbitant amounts of money (at least 2 times the fees of UK/EU students), the situation in the UK with doctorates is quite different. Since doctoral candidates are getting paid, the funding is typically reserved for UK/EU students because the funding body is British/European. There are, of course, funding opportunities for international students, but they are much rarer and competitive. This answer may be of interest to you. I think the US funding bodies are more generous with their funding.

Application: The application process is also very different. In the US, as far as I know, you apply to a department and you don't have to decide on a topic or supervisor for some time. And even then, it's easier to switch topics/supervisors. However, in the UK, when applying for doctorates, you need to write a research proposal and preferably to have already identified a supervisor who can supervise you. Some places even require you to have a supervisor who has agreed to supervise you to support your application. And if your funding is tied up to a supervisor, good luck trying to switch supervisors.

Content: UK doctorates are very focused. There is no coursework, no TAing if you are properly funded (unless you want to), or any of that. Just full-time research on a topic you've already chosen.