I've had both.. a couple of times.
..and with Rancho 9000's and steering stabilizer.
IMO, the air was a little better, but I had issues with the earlier models with air. I'd hope the newer 05/06/07 air bags are better. Maybe some of those woners will chime in with thier luck and off roading with that setup.
I currently have springs and 9000's with tire preassure set at 40psi and it rides/ handles great to me. If you are running higher tire preassure, neither will ride all that great.
The Rancho 9000's make a huge difference to me with either setup.