For work over body fillers, you normally want a "primer surfacer." That is, a high-build primer to fill small scratches and other minor imperfections. "Primer Sealer" is used after you have the surface perfect and just want a uniform surface to paint over. It is a thinner primer and won't fill scratches like a primer-surfacer will. It also helps reduce the amount of penetration of the paint solvents into the lower primer layers.

My experience with rattle can primers is that even the "high-build" primer-surfacers are really thin and don't fill minor scratches well. And they swell when painted over, and later shrink to expose scratches that you thought you filled. Moral of the story: don't spray rattle can primer over scratches more coarse than about 200-grit.