My Western Star tri-axle has Chalmers and I like it a lot. With an air ride cab and the air ride seat, it isn't too bad unloaded (although not near as nice as air ride suspension). It rides real smooth loaded. I do go off road a lot and that is where it shines. I hardly ever have to engage both axles. When one set of tires is pushed up, it drives the other tires into the ground. My buddy with the air ride Pete is always engaging his especially when empty just to get out of a jobsite. Also, there is very little that goes wrong with the Chalmers - cheap to run. And it is lighter than springs and therefor allows for more payload.
I would say the same as the others on this thread. If most of the driving is on road, go with air ride. If a fair portion is off road, go with Hendrickson or Chalmers. I have also heard that the Volvo/Autocar spring ride is very smooth and also good for off road. It is, however, expensive to run/fix etc.