synthetic oils
I have always broken a motor in on the regular stuff and then switched over. I never had a problem with leaks (save for the intake leak which was fixed under warantee) or the car burning it.
Now on which one is better? I have no idea. I think GM knows something since they use Mobil 1 in all the factory Vettes so that has to say something. I don't know if Royal Purple or RedLine is any better or not.

