I'm going to get thrown under the Bus on this one, but I'm a Coil-over guy. I know a LOT of people like Air Bags (Semi-Trucks too), but I don't want to worry about blown air lines, pump and the like. I think Air Bags have a lot to offer (adjustable ride height, load carrying capabilities, etc.), but what if you are in Bugtussle Kansas and a specially made part fails?
With coil-overs you must have well made Spring perches, but the springs aren't that difficult to change if you need different damping. My vote coil-overs-