If your situation is that of internal auditor, your company should choose a method which suits your company.
Most internal auditing courses approximate a Lead Auditor course which focuses on compliance audits. As we know, compliance audits typically involve interpretation of compliance to ISO 9001:2000 [or other standard(s)] by the auditor. Make sure you want that level of expertise and depth.
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My biggest problem with compliance interpretation in internal audits is that interpretations vary widely. Sending someone to a 5 day internal auditor course does not prepare that person for the myriad of interpretations that arise in a typical audit.
I suggest you take a read through https://elsmar.com/ubb/Forum13/HTML/000054.html for some insight on opinions regarding internal auditing.
ISO 19011 - Quality and Environmental Management Systems Auditing Forum Discussions