Searching for the world's best University is like searching for the best cuisine
. Every cuisine is as good as what you make of it. Harvard and MIT in the US, Cambridge, and Oxford in the UK have been at the top in the global ranking for many years.
Universities market themselves like brands so that they can secure a higher place in the rankings. The top Universities have between 10000 to 50000 students, several campuses, and courses from Sciences, Business, Economics, Humanities, medicine. The large and well-regarded universities would give you a competitive environment, while some other universities may give you a nurturing environment. Both are different learning experiences.