Comparing the fallen angelics to humans, which group of psychopaths is the most difficult to rescue and turn back to divine alignment, and why?

We would say that both groups are of roughly equal magnitude in terms of the difficulties. The fallen angels have the longest history of depravity and the greatest extreme of degradation, having come from such a lofty height. The physical humans who are psychopaths have lived that way for a relatively short period of time. Even if they have been a psychopath in many lifetimes, the sum total chronologically is a tiny span compared to the billions of years of misalignment of the fallen angelics, so the karmic disarray is not as severe. But the physical beings like the extraterrestrials, who are perpetrators in your world, have less to work with because they are only a small soul extension, whereas the angelics have a larger portion of the soul to work with functionally, being a light being at the outset and remaining so even though tarnished and defective as a consequence of misconduct, and thereby drifting away from divine alignment and losing that inner connection. But they have the inner structure when healing has happened to have vast capabilities restored within them. The physical beings like humans and the extraterrestrials are in a limited mode functionally, and that is the design of Creator, to keep them contained so their free will choices, even if mishandled, will only be devastating to themselves personally and those others within reach in the physical plane but not capable of contaminating other worlds and the universe as a whole, as can happen with defective light beings. So that is another aspect in terms of the constraints, but representing in the physical beings a less severe potential for causing harm, and thereby lesser karmic consequences of their reach and the things they have managed to impair, corrupt, or destroy. Most human beings alive are not functioning within the extremes of such conduct disorders as we are discussing, and while they might be defective in many, many ways because of karmic wounding and its consequences, their path back to divine alignment is much more straightforward and can be done in a more rapid fashion than for those at the extremes of disconnection like the psychopath.