Well... what are you trying to do? Repaint it to look oem, or just slap some paint on it? How far down did you sand it? To the metal? Just scuffed the clear? Into the base coat?
If you went down to metal you need and etching primer.
If you just just sanded and want to paint over things, most people use grey automotive.
If you want to fix minor imperfections you need a high build primer. (minor imperfections are not dings)