Another vote for the porter cable, you can't go wrong... But notice how some a are forced DA like the Flex, in the sense that no matter how hard you push down they will keep moving. The PC will respond to your pressure. Honestly you dont need much pressure. let the polish do the work. Autogeek.net is a great resource. Also don't go bigger than 5.5 inch pads with your DA. 6.5 will move too slowly and you will not get the correction you want. I'm a big fan of menzerna polishes, less work time, but more aggressive overall. i've been told that other companies have become on par with Menzerna recently.
I'd go with a dual-action polisher. Harbor Freight has an affordable one. Generally speaking start with the least aggressive approach and step up from there. Try an AIO compound/polish/wax with a foam polish pad (blue) or step up to an orange medium cut pad if the paint is hard. There's a lot of good info on technique available on YT .... FWIW, I'm a professional auto detailer.
Highly recommend the Flex 3401 it's safe, powerful enough to take out 2000grit sanding marks and the quality is there as well. Bit the bulliet and bought one this year and haven't looked back. It significantly cuts time down on detailing vs Harbor Frieght DA.
I will be using the mcguirs compound and diamond cut along with an orange buffing pad and buffer from harbor freight. dont spend to much on a buffer, only difference is the amount of vibrations you get from it. pad is what matters