Best:
DFW (Terminal D) - Lots of food choices, fast TSA lines, and free wifi provided by AT&T as well as the train between the terminals makes it easy to change terminals, JFK (Terminal E) was also very nice but very confusing upon navigating.
Worst:
LGA is a nightmare, TSA made me want to cry and the only food I could find was a croissant from Au bon pain.
Best Regional:
DAL, Love Field is clean and easy to walk around, the city of Dallas provided really nice artwork throughout the airport and there are lots of restaurants to choose from.
Worst Regional:
XNA, this was a stopover for me and there was nothing to do and one expensive restaurant with terrible food.