Which part of the quality system is most important?

Quality inspection/Audit is one of the important part as it gives you the superficial view of procedures being implemented as desired for QMS.

all parts of quality is important because if we neglect any part all parts will fail

I will say feed back from the end stage of the product means customer satisfaction, comments and reviews to beginning point at the level of production so I will say communication or the feed back for any product is very important to build up standard quality measures.

This is a very difficult question because there is not a common answers for all kind of the organization. In common Quality System (QS) is for to assure desired functions/expects/price/&all to the customers. So what do customers wants? In fact they want competition and so they want continious improvement from us. Cheaper, more functional, more functions, better design, more effective after sales, more  warranty..

 

After this wiew, we can say that continious improvement and learning organistion is two important parts of the QS.

The most important part of QMS is the internal auditing and Management feedback/action on these Internal Audit Reports/Non Conformance.
this will help in real implementation of the QMS requirements.

internal auditing

Internal Auditing, Control of non-conformity, Corrective & Preventive Actions and most important in my opinion is Management Review i.e.
top management commitment towards quality.

The quality manual

quality ispection

The way they define "quality".