What are the best fast acting treatments for constipation (natural or otc)?

Lot;, what's "best"? Lots of laxatives work fast. What do you mean by "best"?Safe? Active? Occasional or more often use? Why are you constipated? Diet? Inactivity? Lack fluids? Meds? Disease? Stimulants, e.G senna, cascara, bisacodyl, aloe-work fast, crampy. Minerals/saline-magnesium in various forms, phosphate-work fast, can screw up chemistries enemas: (no soap suds) nonabsorbables e.g. Miralax, (polyethylene glycol) slower.