JFK has been the worst in my experience... especially when flying out of Terminal 9 and due to all the construction. Traffic around the airport is horrible, and therefore, the shuttles are infrequent. The shuttle busses have to stop at nearly each terminal... so from the time you drop off your car until you get to Terminal 9 can be up to 45 minutes if the airport is busy. However, as construction finishes, this will improve.
LAX can be good, but usually bad. Waiting for baggage claim in LAX is bad enough... then during certain times of the day, the airport drive can become grid-locked and NOTHING MOVES! When traffic is light, the shuttle ride isn't bad to the rental facilities. I try avoid ever checking a bag when heading to LAX... last time it took me nearly 80 minutes from the time I exited the plane till the time I hopped in my car... and I'm a 5-star Hertz Gold!
SFO has always been tough.... more high tech now, but not any quicker. The walking isn't anything new.... long walks are the norm at SFO... always have been.
SJC was one of the best, but now it's frustrating. Mainly because the rental lots are sooooo lose yet it takes forever to now rent a car and exit the area. (Hertz Gold is off-site, which amazingly, is faster than on-site!)
I've never had a problem with MIA except the maze of streets going from the rental lots to the highways and vice versa... overall, on par with many airports.
As one poster said above, RNO is simply the best! Walk out the terminal and you're there! Very short, very fast!! My favorite!
B.