what do you mean by "private school and to some people that matters"? Do you mean that private school will have an edge compared to public school?
I see, according to US News ranking, UIUC will be the best among those 3 for graduate school in environmental engineering. However after I have some discussion with my US friends, they suggest me to go to either UMich or CMU. The reason is because UIUC is easier to be admitted compared to UMich and CMU and also in general private universities in USA are more respected than public (they mentioned that top universities are mostly private: Harvard, MIT, Yale, Princeton, Stanford, Carnegie Mellon, UPenn, UChicago?) whereas there are only a few of top public universities i.e: UC Berkeley, UMich, GaTech, UIUC, UWashington, UT Austin.)
Regarding the status, I mean when you have a Master degree, will assistantship status give any advantages when you are applying for job?
Moreover, how to check the class size? Is it possible to email the university and asking about this?
Thanks again for your advice, I really appreciate that