My (biased) list:

Easy:
DAY: (rental cars on weekends are so cheap, but I've never actually gone to Dayton)
CVG: A bus that no pax use runs hourly to within walking distance of my house in the city (not in Ohio) that it serves.
GMP: Early AM-> taxis are fast. Otherwise rail.
ICN: I once took an express bus (10 minute wait) to within 1 block of my non-touristy, non-business destination in Daechi-dong. Great if you know how to use them (Mrs. ralfp, born in Seoul, had a harder time than I did). See the quote below.
AIT: It's a nice bike ride. No security,
NGO: Train to downtown. Walk across the street for the Shinkansen.

Okay:
MKE: Amtrak station, but infrequent service that the airlines try to make even worse (like making sure all flights land no more than 10 minutes before the Amtrak departure to CHI).
NRT: Long, but not bad.
LGW
EWR & JFK: AirTrain is nice (stupid rule about no JFK-Manhattan service). I miss US Helicopter.
BWI: Slow light rail. Amtrak/MARC connection via annoying shuttle bus.
ORD: Blue Line went to within walking distance of my place when I lived there. The 1 mile at the end was equally fast by bus or walking.

Everything else:
LGA: Buses are too unreliable. Taxis/car services are more expensive and unreliable (traffic).
HPN: Great for those in the area and with a ride (I just landed there less than 4 hours ago). Otherwise a PITA (parking, if available, is $$$$).

Other:
LAX: Never left the airport
IAH: You have a car, right?