Peyote and aye have been used as medicine by indigenous peoples for thousands of years before psychiatry was even invented. LSD and ketamine do not have the same history of therapeutic use (unless you want to argue that the Greeks maybe drank ergot infused beer, which LSD is derived from). I want to experience these substances authentically by someone who has family ties in shamanism that go back far. It is a better approach to me than trying to will my issues away or continuing to screw off listening to lo fi music in my basement on acid.
Of course, that's not to say that LSD and ketamine do not
have therapeutic use, or somehow have inherently lesser therapeutic use (see maps/past experiments etc), or that somehow a history of such use gives it more merit.
I think it's important to bare in mind that a lot of people are going out to take ayahuasca in ceremonies and being left absolutely jarred to the bones and suffering PTSD etc, with little to no aftercare. I do wonder how different it is than if somebody was giving them 1000 mics of acid or something, often with no previous psychedelic experience.
I just think that people seem to think that going out and doing naturally occurring psychedelics in a ceremony is some kind of definitive silver bullet, when it really isn't the case. It's vitally important to bare in mind that you're being naturally imbued with somebody else's cultural belief system, which might not translate too well when you get off the plane back home.
Not to say it doesn't work or isn't worth doing... but just something to bare in mind. I've come across some pretty pretentious and patronising people who are quite forceful advocates of this kind of route, which doesn't bode well for me. Some of them strike me as little different from priests preaching from the alter or whatever other religious folk you come across trying to get you you to follow their more pure way.
It's great to be open to the possibility of wisdom in other cultures, but I find I am my own best teacher and student.
I'd just like to also echo this statement. But also, whatever works for you.
In the past I have had negative experiences (psychosis) from my DOCs (acid and ketamine), when pursuing a therapeutic experience.
Edit: Just saw this bit. This is something worth seriously taking into account. You will not necessarily be protected from this.
Edit 2: in answer to your original question, my favourite is LSD.