PDCA, 8D or Six Sigma

Problems are seen in everyday life as a real pain and something to be avoided by fair means or foul. In business, problems can lead to low productivity, poor quality, high costs and ultimately loss of customers if the problems are not dealt with rapidity and totally prevented reappearance.
When referring to methodologies for solving problems and not to the tools themselves, here are the most common methods for solving problems: PDCA, Six Sigma (DMAIC), 8D.
PDCA is a methodology of solving problems through Plan (Planning) - Do (Execute, Deploy) - Check (Verify) - Act (take Action). Six Sigma is a data-driven systematic approach methodology DMAIC - Define, Measure, Analyze, Improve, Control to improve an existing process and 8D is a methodology for solving problems in 8 steps (8 Disciplines).