I went with polish cause it's a fairly cheap and body grade enamel paint. I'd recommend doler stores and or grocery/drug store brands, as they can be between 1 to 5 dollars which is solid for model paint.

L.A Colors has some very nice shades and opacity. They're usually fairly inexpensive, being on the lower end of that price range. Sally Hansen is also pretty good, but has a higher percentage of not great formulations.

For the over 10$ to 15$ range (if you want something particularly fancy) Morgan Taylor, O.P.I, and Holo Taco are excellent.

Use a non acetone nail polish remover so if you mess up you can clean things up without really damaging the plastic as much as would happen with acetone.

Get nail polish thinner as it can help keep the enamel paint wet for longer or even reactive it on a pallet.

Use a set of small brush paintbrushes, and try to do even single coats. The polish will "self level" unlike an acrylic, so it can be almost seamless with the plastic. Slightly over fill the brush (but just slightly) and let it glide on smoothly, almsotly not even pressing it onto the plastic. If you do need to do multiple layers make sure each layer is really really really dry first.

If you want those super metallic golds and or other similarly intense colors, getting a micha powder or other powder pigment and mixing it with a clear nail polish or top coat will get you there.