Air Brakes and Air Suspension are specified by the district at the time of purchase - all brands have all configurations.
Air Brakes are typically stronger than hydraulic brakes and can be safer - if there is a leak and air pressure is lost, the rear brakes will automatically apply and stop the vehicle - that's what you see on all big rigs.
Air suspension is not more or less safe than -mechanical spring- suspension, it is smoother and can provide variable lift. There is no such thing as hydraulic suspension on busses. As liquid does not compress, it provides a way of transferring force from one mechanism to another - think big earth movers, backhoes, hydraulic brakes, etc. This would be BAD and a harsh ride in a suspension application. The only application I can think of for suspension would be to raise or lower the chassis from the suspension such as a kneeling bus, but those are typically air driven. Even if there were such a suspension, it would still require mechanical spring or air suspension to smooth out the ride as hydraulic would be like there was no suspension at all.