People are idiots in this thread:
Firstly Oxbridge and Harvard are very different institutions but both are incredibly well respected. No one is going to offer a job to you simply because Harvard>Oxford or vice versa. There are some benefits to both (for instance at Oxbridge you get a lot more personal attention from fellows than you ever would at Harvard). They are also good at different things: you would almost certainly want to go to Oxford to study Engineering than Harvard. The league tables tend to put Harvard top but take them with a pinch of salt - there is a lot they can't capture as all of them recognize.
Secondly ivy>state is wrong. State universities Michigan, Wisconsin, UCLA, Berkeley all hold their own with all the ivies (you also completely forgot about MIT & Chicago amongst others). The ivies are excellent but they aren't necessarily the best institutions in the world. Each one of these universities has a huge number of areas of speciality (UPenn has a great business school, Wisconsin and Michigan are huge receivers of research funds, the californian system has a wide number of strengths, Princeton and Brown are known for their excellent undergraduate education).
Comparing Britain to the US is tough but a number of British universities do hold their own. Oxbridge, LSE, Imperial are all excellent universities for instance. Other British universities have world class departments as well - they might not be able to match universities in the states in every department but that means squat. People get obsessed with ranks when actually very few people in academia care that much