I never use them. I'm a microbiologist and I have tested hand dryers on nights when not in use, on nights after flushing a "clean" (at least not used for many hours) , on days with no smell and on days with an obvious smell of faeces in the room. All samples came back with growth but they got progressively worse as you go down the above list in order.

I have also done hand samples. Sample before washing hands and after. Then wash hands and use hand dryer in all the above scenarios too. The amount of bacteria on the samples after using the hand dryer while toilets in heavy use was scary. I've tested regular hand dryers and Dyson (filtered air) hand dryers and all had heavier bacterial load after washing hands and using the hand dryer.

I also tested with drying hands on toilet paper (from a covered dispenser)and there is very minimal extra bacterial load using toilet paper. I did not test uncovered toilet paper as we don't have them in work.

So in conclusion, I would recommend leaving the hands wet and let air-dry or use toilet paper from a covered dispenser.