I'd go with IAH, better airport.
One of the last few places I never got to, would love to see India. What are they gonna fly there, its out of the range of their 747's,
If they fly nonstop to Mumbai, they'll use a 777-200LR. If they fly a one-stop, they'll probably fly a 747-400. The have 5th freedom rights in Britain, and are not bound by Bermuda II. If they flew out of DFW they could get lots of traffic flying to LHR in addition to the DFW-BOM passengers. DFW isn't on the list of cities which US carriers can fly to LHR.