I think it depends on how durable you want it to be, and how period of a look you want. I think flat acrylics or oil-based paints might get the best period look, as compared to enamels and spray paints. But the latter will be much more durable. And spray-paint with stencils is pretty easy if you're not good with a brush.
But the hardest thing about spray and a stencil is that the paint tends to puff under the stencil, so it's hard to get sharp edges unless you use a stencil adhesive. The adhesive sprays into the underside of the stencil, and sticks it in place. But it's non-permanent (like the adhesive on clear scotch tape), and peels off.
I did this on my shield, and because of the curvature, the stencil still popped up on me, and I still got excess paint. I cleaned it up with an x-acto knife, lightly scraping off the paint I didn't want.
But if you know what you're doing with a brush (specifically how to brush without leaving ugly streaks), you can go that route as well.
