I mean it really depends on what you want to do. If you want to do research, Rush is your school. If you want to do urban medicine, Rush is your school.
I was accepted to both recently, but I'm definitely going to Rush, I want to do clinical research and I want to work with medically under served populations. While SIU does have some of these opportunities, they don't have them like Rush does. I also feel that Rush has some of the best rotation opportunities in the state, I mean Stroger and the Tower? Located in the medical district of a beautiful city. It doesn't get any better than that. Rush also has more resources. I also don't want to live in Carbondale or Springfield, I need something more. If I'm not mistaken Rush students do better on Steps as well.
But that's just my opinion, its still up to you.