The air bags are the way to go, they provide a better ride and are adjustable.
The two major brands are Air Lift and Firestone,which one you decide to go with is really un-important, they are all but identical and the price is also about the same. Both will come with a 5,000lb rating and both mount in the same fashion.
If your truck has overload springs (a seperate spring pack of 3-4 leafs, mounted on top of the main spring pack and seperated by a 3/4" spacer) then you will need to remove them. They are in the way, and take up too much room. The air bags just fit with them removed. Don't worry about removing them, the bags will give you more capacity then the overloads provided and will make for a better ride.
Trucks with gooseneck or fifthwheel frame mounted hitches will need to be a little more creative when it comes to mounting the upper air bag support. The side mounted part of the hitch, which bolts to the side of the frame rail, will be in the way of the upper bag mount. This is not a problem, the upper bag mounts to the frame with 4-3/8" bolts, you just lay-out the mount and drill thru the frame and hitch plate at the same time. I think it makes the hitch better, it has more bolts holding it to the frame. Usually, one or two of the bottom holes on the upper bag mount will not land on the side mounted hitch plate, this means you will just have to drill the hole and use a spacer to take up the amount of differance, usually 5/16". The bags will work just fine, it is just an addittional step or two for the guys with a bed mounted hitch.
The air bags are worth the trouble of mounting them, they allow you to change the height of the truck, and level it when towing. Also, by removing the rear overloads the ride is much, much nicer. In my opinion you should also run a tank and onboard compressor, it allows for adjustments on the fly, and also makes life much easier.