I have been using the paint on water method. I use plain old Rustoleum enamel. You can get gloss, semi-gloss and flat and you can mix them to the sheen you desire. I thin it with real reducer (not hardware store mineral spirits) though I know some people just use it as is. I can't get it to run off as it should if I don't thin it down.
I float the paint on the water by pouring it down a mixing stick or something similar rather than just dumping it in. I also make sure that I have enough depth of paint to coat however many parts I am doing, as your paint layer gets thinner with each part you dip and you don't want to find you don't have enough paint to coat the last few parts. It helps to use a container just large enough horizontally for your parts. That way, you can have a nice deep layer of paint on top without using a lot of paint. Of course, the container has to be tall enough to completely submerge your part.
Some parts are a tricky shape and can trap an air bubble, which prevents paint getting on the part before it touches water. So I have gotten in the habit of putting a rattle can coat of paint on the part first so that even if this happens, it isn't obvious. You have to think ahead as to how to hang the part for dipping as you want paint to run off and not puddle up somewhere. I have found pulleys can be tricky in this regard.
