In my opinion primer is primer. I think that that the real difference is in the viscosity. Just remember that scratch filler will also fill panel lines and emblems. Add paint, clear coat and soon no panel lines
Out of all the primers I have used that cheap Wal Mart ($1:09) is the best. I also like that Krylon Dual Paint and Primer it comes out flat and is a very good. I use the white quite a lot.
Mike