Hello friends, something I can help with.
I’m a “pro” and here’s my current line up.
The Rupes 21 is my bread and butter. Both the Rupes and Flex RO polishers are used/preferred by pros. They offer a blend of high torque and RO to cut quickly but not leave behind swirls. It’s slightly slower than a direct drive machine, but offers much more control.
I use the Rupes 21 and Griots 3” machine almost daily.
The next machine in my pic. is the last generation (2019ish) Griots 6” RO polisher. I used one of these professionally for over a decade for finish polishing work. At that time it was a rebranded Porter Cable.
Finally is the good old direct drive Porter Cable buffer. Heavy and ready to cut heavy oxidation FAST! I rarely use it now unless I’m cutting on extreme heavy oxidation or gel coated fiberglass. This machine has had one rebuild in 20+ years! (It’s also the machine DIYers should FEAR, or at least be pretty careful with. Sucker cuts quick)
To Ramonesfreak’s question, I would steer you to the Griot’s G9 polisher. It’s DIY user friendly. It will cut light “spider web” toweling scratches and halos easily. It will also handle moderate fingernail and “use” scratches.
The backing plate will accept any 5.5” or 6” Velcro backed polishing pad. Whether Griots or a generic.
My go to for general moderate/severe polishing is a foam backed microfiber pad. Cutting is controlled but fairly quick. I use Griots BOSS system of polishes as well as 3M and some boutique brands depending on what I’m working on.
The Griots G15 and G21 are rebranded Rupes machines as far as I can tell. Perhaps some tweaked internals or different cord options?
Undoubtedly robust polishers.
Not really necessary for DIY detailing though.
As others have said here, Porter Cable or other RO polishers are a great option!
Pad and polish selection can also make a difference in your speed and overall results.