The best one is the one that will be accepted/valued by the most customers.
We're in a different product segment, but have done SMETA 4P audits because that's what our customers (Costco and Walmart) wanted. If another customer wanted us to do a ethical/sustainability audit, I'm confident they'd accept that one too.
I laughed at the timeline the people in the Walmart zoom call gave last week. I would expect most companies to need 90+ days advance to get an audit scheduled. When Walmart made the last request they were delusional enough to think we could get is scheduled in 4 weeks then too.
The audit itself takes about as long as all of our routine food safety audits added together (4-5 days for a facility with 1k people). The largest chunk of time is spent in interviews with personnel. The corrective action timeline and report are comparable to most food safety audits.