Salt masking: great for some scales, very easy to over do it.
Liquid mask: I've never met a liquid mask I liked so not too fond of this one.
Hair spray: oh gawd can this do impressive work. Only issue I have with it is the lack of the ability to do complex schemes w/o hairspray between each coat.
Over the top: Meaning a fine brush & or sponge applying the chips over the top of the paint. This works fine for most things, easily switched to various scales, but can take a bit of time.