In Indianapolis, it is WFBQ. As you go north on I-65 toward Chicago, it is amusing to see how far north WFBQ reaches with its 58k watt signal, then around Remington and Rensselaer, WLS starts sneaking in.
This was my experience Sunday driving home from Chicago. WLS was solid until after Rensselaer, then slowly but surely WFBQ began popping through. I didn't keep track of exactly how long the stretch was that the two fought back and forth, but I think south of Remington and Wolcott WFBQ was solid when I was checked back.