Well, I use acrylic paint because oil takes FOREVER to dry. Although I did use oil alot when I was younger because it was easier to manipulate.
However, acrylic is easier to paint over if you mess up lol. It's mostly trial & error until you get the feel of it.
I like to do the background first & tape off what I don't want painted (regular masking tape, & then cut it out with an exacto knife).
For a saw blade, id defeintely use acrylic. I did toybox lids for my niece & nephew a couple of months ago using acrylic. Then I went over it with a waterproof finish from the hardware store. I had to wait a couple of days until the paint was really
dry or else the finish would pull the paint off. I put about 10 coats on each too lol so that it wouldn't chip, because kids are rotten & like to wreck pretty stuff.