As someone who lives in Indy, I like our chances, though it will ultimately boil down to what Amazon values most.
Real estate in Indy is relatively inexpensive, and since we aren't constrained by the ocean, there is plenty of room to grow. Indiana University and Purdue University share a large campus downtown. There are plenty of engineers because of all the IndyCar race teams and all the biomedical companies in the area. There are plenty of scientists due to Eli Lilly and other companies headquartered here.
The suburbs are attract a lot of families as good places to raise kids, while a lot of singles prefer to live downtown, where there is more stuff to do. It's pretty easy to catch a cab, Lyft, or Uber, and the bus service is pretty good (I use it every day). There are also a couple of car sharing schemes for people who want to use a car only once in awhile, but not often enough to warrant buying their own car.
Just my two cents.