If your talking about paint & bodywork, you really only have one option which is an air DA,also known as a random orbit, preferably a "palm" type.
You can switch between 5-6" pads as well as using an interface pad for color sanding clear or primer depending on which. The "handle" style DA's are for roughing out not finish work,so choose yours accordingly.
Air has the option of "infinite" speed controll as well as diameter of the pads orbit.The larger the orbit,the more material removed.When color sanding clear or single stage,you want a small orbit which gives you less material removal and less swirl marking,larger orbit,such as a "mudhog" removes more material in the filler stage but more marking. Electric is fine for roughing out work but not much controll of the speed which is critical later on in the finishing process. There are several electri DA's which have variable speed and these do fine early on or for quick removal of existing paint but really, a good palm sander like a Dynabrade or Hutchins air da is unbeatable.
