The short answer: UIC.
The long one: My decision came down to Purdue versus UGA by April, but then I received a last-minute offer from UIC. Spent some time evaluating and ultimately accepted the UIC offer on 4/11 and declined UGA and Purdue. Purdue responded by offering a one-year fellowship on 4/12 and then a two-year fellowship on 4/13; $20k/year each.
While attempting to process this on 4/13, the tornado sirens go off, the math building loses power, and we all walk down twelve flights of stairs to the basement in the dark. (Fortunately, our math building was built as a fallout shelter.) It ripped up Main Street pretty bad; we even made the Weather Channel!
At this point in the story, there are more tornadoes to come for the rest of the weekend, including those that would ultimately demolish Woodward, OK and Wichita, KS. Evacuate to Dallas; just end up telling Purdue to pass the fellowship on to someone else.
I'm still pretty happy about going to UIC -- their program is a bit closer to my research interests, which is why I picked it in the first place, and I've got a lot of friends in Chicago who I'd already told I was coming. But maybe I can serve as an instructive example to next year's crop that you should always free up the days around 4/15 in case something comes up.