What is the best way? I have never done this but if I get an order I want to be prepared.

Thanks

 airbrush for sure

I have seen it done both ways. I guess it depends on the look you are going for. I saw a video with a lady who airbrushed a little water on lilies and sprinkled disco dust down the center of the petals. It sounds weird but was actually really neat looking. 

My opinion is it depends on how skilled you are w/your airbrush in shading colors.

I prefere dusts myself.