Which would make a better cleaning system water or air?

With water almost all of the particles would end up on the floor. A sloped floor to a filtration system would make the water reusable for the next EVA. The down side is the effect water could have on the suits and tools.

With air there wouldn’t be any damage to the suits but there is bound to be dust on the walls and floor. When you cleaned the airlock this dust would end up back in the air.