This is really far too broad a question to be throwing out like that. I believe that similar tiers of University will have similar standards of education, it would be ridiculous to say that Kennesaw State University is better to study engineering than Imperial.
My understanding from talking to people in the US and the UK is that at a High School level, generally people of equal intelligence from the US are disadvantaged. A-levels are far more challenging than APs by anyone’s gauge and are generally regarded as the least respectful of the 3 big international qualifications (A-Levels, IB, AP). If you were to take an AP student and put them in an A-Level class, I guarantee you they would fail the majority of the modules (this may not be entirely true in subjects like Maths or Physics but those don’t really count)
In addition to this ignorance seems to be a fundamental part of the American Curriculum. I know people currently studying in the States who have got places into top tier universities(Duke, Brown, UPenn) with SAT scores well above 2100 and they knew less about the world outside the USA than a middle income 5th grader, but then again that’s just part of the country.
It’s also worth noting that the US has far more “rubbish” universities than the UK.
Out of roughly 150 institutes the UK has about 20 that are internationally prestigious (with maybe 5 or 6 additional specialist institutions chucked onto that if you’re feeling like it)
Out of several thousand institutes the US has less than 50 that have any significant international prestige. This means a lot of US institutions are pretty much big, expensive degree mills.
Tl;dr :
UK high school system generally superior to all but a few American high schools
This leads to US universities spend the first year teaching stuff you don’t really want to know about at an A-Level standard
Considering the costs of US universities in relation to UK universities, even for an international student, this is a huge waste of time and money
This means that an Undergraduate Education in the UK will be in far greater depth than a corresponding one in the US, however, the US candidates might have an edge on you on stuff like basic Spanish or simple Economics.
Its worth noting that most of the big US institutes are renowned for the quality of their Graduate degrees ( Harvard Business, Yale Law, John Hopkins Medicine) Whereas the UK is more even across the board.