The homer in me wants it to be...
1. Navy Pier. You can't really get much more publicity than one of the most famous shopping malls in the world. Hotels aren't too far from the Pier, public transportation is relatively reliable for such a large city, and parking isn't terrible in price.
2. McCormick Place. If you want pure size, it'll be difficult to go much bigger than this. They hold an auto show here every year, with virtually every auto maker in the world participating in some way, shape, or form. The hotel situation nearby isn't terrible, and there's some pretty decent transportation options in the area.
3. Donald E. Stephens Convention Center in Rosemont, IL. This is my personal favorite place, even though nobody ever thinks about it. The rooms are massive. The hotels are close by, and a couple have skywalks to the Center. There's reasonable food fairly close. It's RIGHT next to O'Hare International, just hop on the subway from the airport and it's one of the first stops you come to. And parking is very reasonable if you know where to park (subway station, $5). They hold Wizard World Chicago here every year, and there's plenty of room for that massive convention.
Though, I agree that Indy was a fantastic choice for everybody involved. If it's not going to be moved to Chicago, Indy is probably the best choice I can think of.