Anything that forces you to come to terms with yourself (and any shortcomings) is the most valuble in my opinion ('in your face' psychedelics like LSD) as ones that are more malleable allow you to hide from aspects of yourself that might surface. These are the sort of things that need to be confronted if you want to become a 'better person' (not everything valuble that comes from psychedelics is all 'oohs & ahhs').
The more malleable ones are possibly better when it comes to emotional insights, but for getting to the core of something deep you need the sort that have that 'you can run but you can't hide' quality. Of course they tend to be the ones people can be fearful of as if things take a downward turn during the experience, you are forced to go with it and experience aspects you'd normally avoid at all costs