For a larger vehicle, air is preferred. First.. safety, if you lose your air the spring brake will stop the truck. If your system leaks and won't build pressure you can't move it from the driver seat.
Second... There is no fluid to sit in lines and corrode or if it sits for long periods, degrade.
I like the air brakes on my bus.
They do take a bit to get used to. You don't have the same feel as hydrolic.
All that being said, hydrolic brakes can stop a full sized bus.
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