Atlanta Hartsfield International is traveler hell. If you have a connecting flight and don't have an hour between flights, god is the only entity that can help you. All transportation is automated, but there is only one train that runs between all seven concourses. Each concourses has around 36 gates and you could end up literally walking several miles to get to your aircraft. With arond ~2,700 flights per day, there is no easy way to organize this place. All WiFi is charged by the hour. The good news: this place is so busy that you'll find some kind of bar or eatery open at almost any hour.
Tampa International - By far my favorite airport and was long before I moved here. Difficult to get lost, parking and finding your car is simple, and all transportation is automated (except for the new, long term deck) with each airside having a dedicated train. Free WiFi throughout the entire airport, too.
Dulles International cracked me up because the airsides are removed from the terminal and no trains link them. How do you get to your flight? You climb aboard a large, raised bus that drives across the tarmac. Atop the bus are massive, white fins that help the vehicle be noticed by taxiing aircraft, giving the impression of people-filled sharks traversing the airport. Ground traffic can easily delay you.
Worst airport people mover, ever!