I've transported camera gear in handlebar bags, on racks, backpacks and jersey pockets. They all work.
My preference is a rack on the back, or rear panniers with a rack. I find that a backpack makes you top-heavy, and gets uncomfortable after a while.
If the cameras have some padding and are secured, a fall from pannier height, or even rack height isn't a problem.
If they are going to fall, I'd much rather it be from a 3 ft/ 1 meter or so than from 6 feet attched to me.