I fly out of IAD all the time and occasionally out of ORD. I have not noticed much difference in lounges between the two airports. After all, what can you do with a carrot?

As Tom Beyersdorf said, the trip to your domestic gate is longer at ORD--but I have found ORD to be better for immigration and baggage. It's a toss-up. I'd make my arrangements on the basis of other concerns (schedules, prices, layover times).