When I use masonite or wood, I like using shellac to prime the surface. It doesn't have a lot of tooth like gesso, so the paint seems to sit on top of the surface and really makes brushstrokes stand out. I like working that way, but I do know there are a lot of people who dislike it as well. If you prefer gesso primed surfaces, I prefer to do the multiple coats with in between sanding. You get a really nice finish with some good bite to hold the paint.
If you go for masonite, make sure it's oil pressed. The other stuff isn't much better than cardboard and will soak up moisture like a sponge and crumble. The oil pressed works great though!