First, I suggest that you not get too worked up about this. If you do the fundamentals of "success" (develop technical knowledge and skills, build social capital, work on interesting problems, etc.), you will be a success after graduating from either of these schools.
Second, I would focus most on where you want to live geographically both during school and after -- this will drive a lot of your happiness in life. UIUC grads will have an easier time landing jobs in the Midwest, and UVA students will generally have an easier time finding jobs along the East Coast (esp. mid-Atlantic).
Third, neither of these departments will hinder your intellectual development. Hands down, you yourself will be your biggest limiting factor (the big winners at good schools are folks who embrace autonomous learning). That said, I suggest you look at the research projects/programs/centers led by professors at each of these schools and see which ones have more projects that make you say "hell yeah!". Go to that school and try to work on one or more of those projects. Figure out a way to be useful to the lead researchers ASAP and possibly start working with them now or this summer.
If you still can't decide after doing the above, I will add some marginal issues for each school:
UVA
+ Scholars programs sometimes have unstated benefits like access to jobs, funding, or social contacts. This is potentially big (not sure at UVA specifically).
+ Priority scheduling is a big deal at big schools. Avoiding crappy profs makes school a lot more fun.
UIUC
- The state budget is in shambles, and the school has had some upper administration issues in the recent past. The school is currently not in a great place organizationally as it has been in the past.
- Relies a lot on international students (which is cool imho), but the students and their funding may vanish rather rapidly if the US is perceived as being hostile towards immigrants. This has the potential to create a bigger administrative mess.
Let me know if you have any other questions, and I will be happy to answer.