You may rethink about whether you like math or not. It is quite important in research. I will agree with Kevin that UIUC will be a good choice, although I am not sure about the master program there.
The time period of giving offers should be same. One thing I want to mention is that OB, IB, marketing are relatively practical compared to economics. However, practical is not equal to meaningful. Doing research for most researchers is for pursuing pure academic interests, and practices are not important. It may be better for you to read some academic papers in order to know what academic research is.