I’d say Peru is probably the place to go. Ten years ago we spent a good amount of time around Pucallpa and Iquitos traveling and learning from local teachers. A lot has changed since then– the gringo resorts have popped up everywhere, so it really depends on how much you value ‘comfort’ over authenticity. Best is word of mouth and you probably won’t find a genuine curandero online. Doesn’t make either experience better or worse, just different and ultimately depends on your goals, willingness to fork over a load of cash, working knowledge of Spanish, etc.