One thing you need to be aware of is not to leave the polisher, whichever one you go for and personally I have Meguiars, in one place for too long, keep the pad moving on the panel and don't let the polish dry or you'll do more harm than good. Personally I go over a panel twice the second time at 90 degrees to the first, left to right and then top to bottom.
Polish you let dry out, cutting compound you don't let dry out, either whilst polishing or before you take it off, buff it off before it dries, this is not from me but from a demonstration by a guy from Meguiars at a Porsche owners club day.