I'm sure that some guys that are a little more up to date on the 3M products will be by to help you out. In the meantime, I've heard a lot of good things about the Perfect IT III Machine glaze, and the Finishing glaze.
Depeding on the scratch you start with more course products obviously. For 3M products i find the answer simple. There PI III line up is pretty great from my experience. For serious scratches use the PI III extra cut or light cut compound with a rotory and cutting pad. Then move on to the PI III machine glaze with a rotory and polishing pad. If you feel you need/want it go onto the PI III finishing glaze with a da or by hand. That should be all you need.
