I haven't looked into air shocks. I'd like to hear some info on those... Maybe Iz will chime in with info on his.
When tuned, the ride is quite amazing due to the wacky spring curve which you can twist and bend to your liking with the proportion of oil, nitrogen, valve stacks, and the "negative" spring in the shock (this spring would have to be custom as Fox only sells one type). The shock itself is very easy to rebuild and replace parts if needed.
Speaking of tunning, I hope Spas gets this one particular video to me soon because that demonstrates an air shock that is NOT properly tuned. In that video (taken at the last M&G), my truck thought it was a trophy truck and upon acceleration, the front would rise about 10 inches -- wacky ride! If such a suspension were taken off road, it would probably flip the vehicle with a little bit of gas on an uphill rock climb.
I drive my truck maybe 2 or 4 times a week and after about 2.5 months and one drive to Paragon (360 miles total to and fro), the shocks needed to be refilled with nitrogen as the ride height decreased by about 2-inches. But this is not a big deal as recharging takes just a few minutes.
Like any other shock, air shocks "leak" oil at the bottom -- thats just how they lubricate the bearing and bearing seal. So they must be recharged with oil too every half a year or so (or at least thats my guess from the measurements I took of the oil volume).
Also, like any other shock, try not to get brake fluid on the shock. It eats up the seals and that is my problem right now and that is why I have my air shocks dissassembled (
http://www.explorerforum.com/forums/showthread.php?t=172089).
The initial cost when compared to a coil-over is a somewhat lower as a pair of Fox 2.5 Air Shock can be had for $700. Don't bother looking at the 2.0 Air Shocks because those won't support an Explorer's wieght. Of course, in the long run, you will need to acquire a nitrogen tank, a high-pressure regulator for Nitrogen (max air shock PSI = 350), the proper hose, and a schrader fitting. A gallon of Fox 5-weight oil also typically costs around $30.