English-speaking kids: private or public schools? (Vienna)

dear all: perhaps this question is already answered in one of the blogs so my apologies if I am asking the obvious. I am considering a move to Vienna in the next few months and have 3 children ages 11, 9 and 2. My 11yr old girl is a 6th grader at a very good American school in Brazil, and my 9yr old boy is a 4th grader. I am now looking at the Vienna International School, at the American International School of Vienna, at the Vienna Elementary/European School (Landstrasse 75, Protected content , and at the Danube International School. Should I also consider public schools (English speaking, bilingual)? My kids are fluent in English and their native tongue is Portuguese. They do not speak German. Any comments on the private schools above? Pros and cons? THANK YOU!!
Romero