I chose UIC over SIU based on location.
School is going to be school regardless of where it is. Chicago simply offers more than alton in terms of things to do. A lot more actually.
The ADA has its headquarters in the city, the midwinter meeting is held in the city (students are invited and can volunteer to work if wanted), your networking potential is expanded by simply being in a saturated area.
Really though, it doesn't make much a difference education-wise. Just go where you want to live for four years.
Others may diasgree, but very few people attend more than one dental school, so any comparisons will be pure opinion (as is this post).
Congrats on getting in, and good luck with the decision.
ps. I also prefer DDS over DMD.