Quality difference between print directly to pdf, and print to ps and then convert to pdf

I notice a big difference in document quality between these two techniques: When I print directly to pdf using Autosave format 0, the final pdf looks very nice. However, when I print to ps using Autosave format 6, and then convert to pdf using "cConvertFile", or even Acrobat Distiller, the image quality is much worse. Also, the text is not selectable anymore, so I think the text is treated as an image. I actually need the ps, but in better quality, not the pdf, so does anyone know what I might be doing wrong? Thank you.