These three products by 3M should be on every garage shelf. Mine have been used for years, as you use so little each time you have a scratch. You can use them with a buffer if you use the correct pad for each. Your local body shop supply place can sell you these, and tell you which pad to use for each.
I had a new scratch that I found yesterday that looked like someone intentionally took their ring, and rubbed the front fender for about 2 inches. You could feel the scratch with your fingernail, and it was solid white against my dark green paint...UGLY! I used a couple of Shop Towels (the blue paper towel like ones) as I was doing such a small area.
Start with the Extra Cut, and a little elbow grease (if you are using a buffer, be careful with this, as you can go too deep!). Once the scratch is smoother, hit it with the Swirl Mark Remover until the paint looks shiny again. Finish up with the Ultrafina, and most scratches will disappear! Mine did. Great products!