to me the biggest concern would be Heathrow. After recent experiences I would avoid it if at all possible. I could die a happy man if I never set foot in LHR again.

I flew FRA - LHR - ORD a few weeks ago. I ended up going through security three times! Twice in FRA and once after getting off the plane in LHR!

Make sure you read up on Heathrow and their insane policies before voluntarily flying through there.

Also, if you go through LHR don't book the last flight with the 1:20 connection. You aren't going to make it and good luck trying to get AA to pay for the hotel.