i always liked caespitosa, because it looks incredibly easy to propagate at an exponential rate (Assuming you got enough pereskiopsis).
jourdaniana is cool too, because it is the only loph with spines (it is thought to be a hybrid of williamsii and turbinicarpus lophophoroides - idk if that would affect the psychoactivity), and it pups like mad, just like caespitosa - and it has a purple flower, rather than pink (Which most lophs have)
apparently grafting reduces alkaloid content, but i highly doubt that can't be fixed by stressing the plant.
as for the hardiest species, and easiest to grow:
i would have to defer you to hostilis, or one of the other loph experts.
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