2 quistions about saving in PDF-format

Hi There!

When I want to save a document as PDF, it seems that there are about 9 versions to save as PDF. I have these: (1) Archiring (CMYK), (2)  Archiring (RGB), (3) Current Proof Settings, (4) Document Distribution, (5) Editing, (6) PDF/X-1a, (7) PDF/x-3, (8) Prepress and (9) Web.

I'm not sure I understand the explanation from CorelDRAW X6, so I just wan't to know what version will be a PDF in the best quality?(I would be happy if you as a bonus could explain what the other PDF-versions are used for)

About (5) Editing, is that the only PDF-format that can be used by others to edited in?

Thanks for your help in advance.

Jesper Kragh(Denmark)