They are all so unlike each other that such a comparison would be largely erroneous. However, I will say this.
DMT is, by far, the most
overwhelmingly visual psychedelic I have ever used. It literally summons an entirely alien landscape in front of me for ~5 minutes or so, a dimension of impossible form and full of chattering, ancient intelligence. But it leaves my mind completely alone, my reactions are not magnified nor do I have any unusual perspectives. This is not to say that I am calm or detached during the experience, it is just that I am reacting in a similar way to how I would if hyperspace began spontaneously bounding through my kitchen window.
It is entirely different with the little mushrooms. They pour into the skull through the auditory system, a flood of tiny voices that then stimulate flowing visions. I notice a more human-concerned nature to the mushrooms, and a conversational quality in the visions/intimations that is not so strong with many other allies. What I am saying is, questions can be asked of the mushrooms, and answers will usually be given; whether the answers make sense at the time of revelation is not so certain.
The cactus-spirits are an emotional-visual-psychological whirlwind, very arresting and
very wise. Giants among deities. They grab hold ones emotions, magnifying every thought and feeling tenfold. They reveal the knowledge of cacti, the sit-and-wait-and-grow-and-learn wisdom that comes with growing on mountaintops and in deserts for decades. The visions are electric, coming out of magnified thoughts and emotions; they are plasmoid and crystaline. These spirits do not let go. They stiiiick arouuund. By the end, fatigue can cause the visions to break down into the classic "mind-melt" symptoms. I would use more caution using mescaline or cacti than I would with DMT, ergolines other than LSD, or psilocybe spp., simply for the fatigue and longevity of experience for mescaline. I have not yet used ayahuasca, so I cannot say how cautious I would be of it.
Salvia Divinorum has a similar duration, but the effects are not comparable in any coherent way. They are really very very different, opposite ends of the spectrum. DMT is noon-sun-magic, Salvinorin alpha is full-moon-magic. For my psychic set-up, DMT's warming sun magic fit much better. Only a few days ago was I able to work positively with Salvia, after 3 largely terrifying and one difficult experience, though now that we trust each other I believe the little leaves will be a great ally.
Incomparable to any of the less-than-visual psychedelics that I have used, Ipomea spp./HBWR, A. muscaria, MDxx, DXM, PCP, or Sinicuichi.
بسم الله الرحمن الرحيم
Fairly responsible Kratom user.
"whenever he drank ayahuasca, he had such beautiful visions that he used to put his hands over his eyes for fear somebody might steal them."
in between the grinding-brakes of a train crash while aluminum-foil robots make obnoxious sex noises on a static-filled walkie-talkie radio.