This is an age old argument. I have had exactly the opposite experience with air bags. I have installed air bags on almost all of my vehicles for the past 25 years and have had no failure or problems. Every big rig on the highway has air bags. I did break a coil spring on my Rubicon though, it was a early kit from Full Traction and I think the coil had not been properly hardened.
If you carry various amounts of weight at different times, air bags are almost perfection. Now on my 100 as on my 2003 4Runner, I can't see the bags lasting a long time due to the fact that they have to rub against the coil spring and under full compression run the risk of getting pinched in the coils. I will be keeping my eye on them and if need be on the 100, run an air bag that is separate from the coils.
Unless you always have all your gear in your rig, no coil or leaf will be perfect. Adjustability is the name of the game. I tow an off road trailer with tongue weight and then unhook and go exploring. I also have bags on my trailer. They allow me the comfort of lowering my trailer once I get into camp so that when I get to level, the trailer is not four feet in the air.
Just my .02
Jeff