Last year (2016), I applied to several universities in Europe for a master program in Computer Science. I had a look at several university rankings that I found on the internet and computed an approximate weighted average considering how reliable each of these rankings seemed. The rankings were not focused on a particular type of program (and some were not even focused on a particular area like Computer Science), but a reasonable assumption is that the better a university’s overall ranking is, the better all of its programs are. According to this subjective ranking system, I would order the universities you mentioned as follows (starting from the best): Cambridge, Oxford, ETH Zurich, Imperial. These are, in my opinion, together with EPFL Lausanne, the top 5 universities in Computer Science in Europe at the moment.
I applied to the first three universities (and EPFL) and got accepted to all of them. I decided to go to Oxford and switched to a master by research in the last minute. However, I had to do two taught courses and had a lot of contact with the taught master program (my girlfriend is doing it). I think there is a good selection of courses and the most popular ones are taught almost irreproachably.
Assuming that you are interested in applying for a master, I would like to mention an important point which I overlooked when I decided which university I would join. You should check out the departmental websites for each of the universities you are applying to and find the list of courses that are available in the next academic year. Carefully study their description and decide which ones you would take. You will eventually have to make this decision anyway and you shouldn’t get into a position where you don’t find enough courses that interest you. Looking back, I realized that this would have probably been the case for me if I had gone to Cambridge.
Finally, before deciding to go to a university in Switzerland you should consider whether the language is a barrier for you or not. Even if the courses are taught in English, you will need to speak German (or French) for even the most basic things like shopping for groceries. Learning a new language may not be as easy as it seems, given how stressful the terms are at the top universities.