If there's only two of you, I'd vote: none. The Palmer House will give you a tiny room if you are without status. The Hilton is a bit far south. The 4 Points is in a good location, but something about it from the outside gives me the creeps.

I'd book a refundable rate at the Four Points, but then I'd go to betterbidding.com and research Priceline rates for 4* properties the "North Michigan Avenue" zone. Unless there's a convention in town, $65-$95/night will likely get you the Sheraton or the Hyatt Regency, both two blocks east of Michigan Avenue on opposite sides of the river.