You might want to consider, in addition to costs (and the rankings), whether your education to date is recognised as eligible for ETH entry at Bachelor level (unless you are looking at Masters...). It is generally much "easier" (this being a slight euphemism) to enter graduate level than undergraduate if from a country other than CH. This may vary according to program/department (best to refer directly to http://ethz.ch .
Is the German study in Vienna pure and basic language? (minus the quirky dialect that almost makes Swiss German understandable in comparison)
Yes thats why I am asking.Because in Zürich I will pay two/three times more but is it worth it.
I like it and I am really interested in it,mostly in creating mobile applications.
I am almost sure that the ETH offers the courses I want.
I also have a lot friends that want to study CS and have no clue what they are studying.
How are the things with the master degrees?In their web site it is written that the master in CS is only in English so this fact makes me thing that there are many people that want to do their master degree at the ETH?How do they choose who to study and who not when there are no exams?
Then get out there and write some. I doubt any top university CS course will spend much time on mobile app writing. Are you sure it's really CS you want, or something more blended with business, media etc. I don't know, but I would expect especially at ETH the CS course is more maths/theory oriented and for programming elements will include bits of various 'exotic' languages which are less likely to be of direct use commercially. Remember the 'S' in CS is for science, not programming/app writing
Courses at ETH are top notch, and taught by some of the professors who created the sub-domains itself. It's can be as practical as you want, depending on the courses you choose.