Air springs
provide the most comfortable ride, but have multiple points of failure (airline, compressor, air bags, fittings).

Suspension Modifications

It is very uncommon to modify a your suspension from one spring type to another due to the difficulty and cost involved of changing the mounting points but air bags are sometimes added to other spring types to improve ride height under load.

Shock Absorber Types

The main types of shock absorbers are fluid filled, gas filled or foam cell.
Fluid filled shock absorbers
used to be the standard on all vehicles, but are being replaced by Gas filled shock absorbers as standard on most modern vehicles. The problem with fluid filled shock absorbers is that as the shock works hard, the temperature heats up and the fluid becomes less effective, so that the springs cause the vehicle to bounce. This is a dangerous situation.
Gas filled shock absorbers
are becoming the standard on most modern vehicles. Gas can tolerate much higher temperatures than fluid before losing its damping effectiveness.
Foam cell shock absorbers
once the domain of competition vehicles are becoming economical enough to be worth consideration for those enthusiasts who want the safest possible shock absorbers for their life style.

If you wish to improve your vehicle for load handling, comfort, performance, safety, or any combination of these factors, then you should seriously consider upgrades and modifications to springs, shock absorbers or your whole suspensions system.