Well yes, i know that. Obviously any Psychedelic has the potential to induce a bad trip and/or frightening psychosis. I'm trying to find out which would be the least dangerous besides that factor.
Again, physiologically speaking, most (assuming we are talking just psychedelics and not hallucinogens as a whole) generally carry the same weight in "physiological danger", which isn't very much at all. There are some exceptions, such as bufotenin, Bromo-DragonFLY, 5-MeO-DMT to a degree, etc. Also, the "research chemicals", which includes the aforementioned Bromo-DragonFLY and 4-AcO-DMT, don't have nearly the same proven track record as other psychedelics that have been established for much longer such as psilocin (shrooms), mescaline, and LSD. In fact, some of these have been proven to be pretty sketchy, especially the ultra potent ones like, again, Bromo-DragonFLY. 4-AcO-DMT so far appears to be safe, but it's also too recent to have had much in-depth study made on it, but as no serious side effects of its use have been reported so far after being around for a few years, it would seem logical to conclude that it at least isn't as dangerous as, for example, mephedrone (which isn't a psychedelic by the way, just another RC), which had serious adverse effects stemming from its use reported soon after it hit the market.
However, as most/many psychedelics have vasoconstrictive properties, they could be a bad idea if you have high blood pressure. Some psychedelics such as LSA (from Morning Glory seeds or Hawaiian Baby Woodrose seeds) can be far more potent vasoconstrictors than others, including the related chemical LSD.
As far as physical
discomfort, mushrooms have a tendency to cause significant nausea. This can also be the case with mescaline. LSD is likely one of the most gentle psychedelics on the stomach there is. They can cause muscle tension though, and sometimes this factor bothers me a bit with LSD in particular.
Mescaline is generally cited as being one of the best choices for a beginner psychedelic due to its relative ease to handle. It's also not nearly as available as mushrooms or LSD, which is why people often start with one of those two.