Last summer when based in Japan I had a business trip in upstate NY so I flew via IAD. At that time of year it lands close to peak European arrivals. I think my flight was just a little bit late. I am sure that immigration was really busy but whisked through using Global Entry. But then I hit the transit security; probably 30+ minute wait and I am sure foreign visitors had waited already more than an hour for immigration. It was hot (weak AC) and many passengers with really bad BO. TSA was making everybody go through body scanners. I think that I flew United First but that was not good enough; United was only letting people with Global Services jump the queue. Then I got into an altercation with a TSA goon; always happens when try to put me through the body scanner.

I should have gone to the main terminal. One has that option if there is no checked luggage.

Good airports for transit are SEA, LAX (with UA), SFO (with UA) and probably DEN. But flying a transcon to PHL is not that attractive. I would go to EWR and travel by car or train if I had a child with me.

p.s. Check the airline websites directly. Matrix.itasoftware.com is a good tool for multiple airlines. You can get a 5 day free trial at Expertflyer.com and check the actual fares for the market. They will be quoted without tax and fuel surcharge.