A paint polisher is a necessary tool for removing scratches from your vehicles finish. Trying to remove defects by hand is sometimes possible if they are extremely fine, but its hard work. You will never achieve the same results by hand as you would with a polisher.
There are two types of buffers, random orbit and rotary (circular). There are many different brands available for both machine types. The most popular rotary polishers are the DeWalt 849, and the Makita 9227C. The most popular random orbit buffers are, the Porter Cable 7424XP, Flex 3401VRG, Meguiars G110v2, and the Griot's Garage 6'' orbital.
I have used all of these machines except the Meguiars and the Griots, and have had positive experiences with each one.
Random orbit buffers are really capable machines, however they aren't as powerful as a rotary. Therefore they take longer to remove scratches.
If you are a beginner, I strongly recommend using a random orbit
polisher. The benefit of these machines being less powerful is that they
don't produce near the friction/heat that a rotary would. Though less heat makes
it more time consuming to remove defects, it also greatly reduces the risk of
damaging the paint and virtually eliminates buffer lines, (holograms).
Random orbit polishers are great for removing moderate defects, applying finishing polishes, waxes, and paint sealants.
For more aggressive defect removal, and quick removal of wet sanding marks, a rotary polisher is the tool of choice. Being that its much more powerful than a random orbit, and the pad spins in a circular motion, more friction/heat is produced.
Heat and friction combined with a good polish and pad will make quick work of
the damaged area. Rotaries aren't just for defect removal. Once you get
comfortable with the correct operation, they can also be used for finishing
polishes and wax application if you desire.
Due to the added weight and bulkiness of rotaries, I personally like to finish
the polishing process with a random orbit buffer.
1968 Oldsmobile Cutlass, wet sanded with 2000 grit paper. Polished with my DeWalt rotary polisher.
My advice is to get comfortable with the polishing process with a random
orbit buffer first. Once you are confident and ready to purchase a rotary,
grab a hood or trunk lid from a junk yard and practice on it.
Get comfortable with the characteristics of a rotary paint polisher. Try to
remove all the scratches from the junk yard panel. Add new ones and remove them!
Experiment to see just how fast a buffer will go through the paint on the edges.
See how hot the paint gets if the machine sits in one spot too long. Discover
how easy it is to burn the paint if you aren't careful.
Knowing what the rotary can do, good and bad on the junk hood, will really make polishing your vehicle a better experience.
Practice makes perfect, just remember to keep your pad as flat as possible
while buffing. When using a rotary keep the rpm in the 1000 to 1200 rpm
range. Once you learn the art of polishing, you will never want to attempt
hand polishing ever again!
Here the Oldsmobile paint has been finessed using my Flex orbital buffer.