If you're looking for a straight comparison for the AA 787-8 and 777-2 refurb..the 787 is quieter in my experience and the business cabin is smaller. Service, meals and seats would all be similar other than that. The other biggest factor is connections and layover timing. Dallas lounges are, in my opinion, better than ORD. Also, depending on time of the year DFW is a safer bet due to weather in ORD.