I would say as far as sanding goes, PLA would be the easiest to sand, and ABS the hardest due to PLA being a relatively soft material. However, you can use acetone to smooth ABS parts very easily, minimizing the amount of sanding that needs to be done. Printing at a higher resolutions would lower the amount of sanding that needs to be done, but raises the print time. If it were me, I would print with ABS at 200 microns, and use sand paper to smooth initially, and then acetone to get a glassy finish before priming and painting.