I agree with Nigel that US universities are the best in the US....
As for ranking of educational establishments, the positions are normally determined by numbers reaching certain academic levels. Fair enough in one way. However, this doesn't take into account the material that diffeent establishments have to work with. Harvard is bound to have better academic results than Bloggsville University, Wyoming, because more of the 'top' students will go to Harvard. Bloggsville may in fact do a marvellous job of taking sows' ears and producing silk purses, but the value added isn't taken into account when the rankings are done. The same occurs in the UK with Oxford and Cambridge. I suppose the money factor comes in a bit with both the Harvard / Oxbridge intake, but very often the monied ones do have brains - otherwise the money would run out. (Doesn't always apply - you need a lot of money to become US President, but seemingly you can get away without much in the brain line.)