I do both, depending on the size and contour of the panel.
If you use a machine, it all depends on the speed and orbit size.
I find an electric random orbital sander I normally use for woodworking
works best, you have to turn the speed down to about half and then
it works amazingly well. A DA never worked very well for me.
For collision work I hit 1500 on da w/ norton dry ice then will nib out dirt specks then wet 3000 and buff. For resto or high end work all blocked by hand and maybe 5000 da damp. No 2 jobs the same. I know a resto shop only does old Buicks will sand wet 1200 then buffs and buffs his a** off but nice work.