Hey, great question, feel free to PM me for more details -- I am a Chicago resident, applying to med school this cycle.
The most fatal mistake I made when choosing between undergraduates was "which school is ranked highest in the major I was interested in?". You'll note that these arbitrary rankings are there mostly for research; it is usually graduate students and/or professors who are looking for a position who should look at these things somewhat seriously. So, just because one school has a higher ranking doesn't mean that you should go there -- maybe you will decide to major in something else (aka what happened to me in college).
As a pre-med, I know students who have went to each of the three undergrads (UIC, UIUC, and Loyola). I think each of them has their own advantages and disadvantages. I say UIC is a strong choice because it is the only one with a medical school literally right next door. Loyola Chicago is a bit of a ride from Loyola Medical Center (Maywood, IL). UIUC doesn't have a medical school except for Carle Illinois, which has an engineering-based medical curriculum. I do believe that strictly undergraduate reputation wise, UIUC has more of a name than UIC and Loyola, and this may be partly because of UIUC's absolutely stellar engineering reputation.
I don't think you are hurting yourself by going to any of the three schools. You should look and talk to students about their experiences. UIUC has a very large student body and has had more students who have been pre-med and gone successfully through their curriculum and then matriculated to UIC and/or Loyola med school as well as other schools nationwide. The pre-med curriculum will be the same (take the core required courses).
You should ask yourself what you want out of college - how much you prioritize a hospital nearby for volunteering/research, how much you want a well-rounded education or want to do engineering, finances (which one gives the most aid), etc...
And like the previous poster said, your experiences and what you did in college (most importantly GPA and MCAT) are more critical than school's name. If you want to know which school looks best reputation wise, like I said before, it's UIUC in my opinion.
Good luck!
