I wouldn't use either on a BRAND NEW CAR. A Good washing and claying should be all the prep you need unless there are swirl marks or scratches that you would like to remove. If that was the case, AIO or PPC wouldn't remove them anyhow.
PPC is milder than AIO. Again this is just a educated guess. The biggest difference is that AIO is a one step "cleaner wax" type of product, while PPC is just a polish that adds no durability.
Whatever you decide, you can't go wrong....just make sure if you use PPC and SG with no AIO that you wash the car in between steps to remove any oils or fillers.
