I can only answer regarding DFW
On the southeast corner of the airport, near the DFW
administration building is a spotter's park known as "Founder's Plaza". It has parking for 20-30 cars, binoculars, and a live feed of the arrivals frequency on a speaker.
If traffic is arriving from the south and you're there before 3pm, you should get some great shots. After then, the sun will be shining in your face.
Also, on the west side of the airport is the AA
maintenance complex and the American Eagle office building. The parking area by Eagle faces the terminals and the two parallel runways on the west side.