In terms of airport hotel convenience and quality, I would pick ORD (Hilton connected to the terminal, Hyatt choices, etc.) unless one plans to stay at the TWA Hotel at JFK.

ORD has bad roadway construction and changing between T1/2/3 and T5 (international) is horrible; airport hotel shuttles might not go to T5. OTOH, changing between most terminals at JFK isn't pleasant or convenient either (but there are some tricks, such as walking between T2 and T1, taking the airside shuttle operated by DL called the JFK Jitney between T2 and T4, where many airlines use the enlarged T4). I'm not sure whether the airport hotel shuttle buses actually serve the terminals at JFK or force one to use their landside train, but off property hotels at JFK seem bad in general.