I was actually thinking about this topic last week, so it was a welcome surprise to find this thread.
I did some searching, by no means exhaustive, but I did focus on those cacti that are used predominantly for fruit production, not those that are incidentally edible-fruited (with good flavor).
The best for edibility (in no particular order) seem to be Prickly Pears (Opuntia spp.), Bilberry Cactus (Myrtillocactus geometrizans), Apple Cacti (Cereus repandus/peruvianus; also C. jamacaru, C. hildmannianus), desert Pitayas (Stenocereus queretaroensis, S. thurberi; also S. griseus, S. stellatus, S. pruinosus, S. marginatus, S. gummosus), Dragonfruit (Selenicereus undatus, S. costaricensis/polyrhizus, S. megalanthus, and hybrids), and Barbados Gooseberry (Ora-pro-nobis as a leaf vegetable, Pereskia aculeata).
Honorable mentions include Saguaro (Carnegiea gigantea), Cardón (Pachycereus pringlei), Leuenbergeria (Pereskia) bleo, Rhodocactus grandifolius (leaf vegetable), and Epiphyllum hybrids (Disocactus; there was a thread here that singled out “Argus”, “Padre”, “Daybreak” and “Fern La Borde”).
Here’s a Spanish article about the fruiting Stenocereus:
https://huerto-en-casa.com/pitayas/Here’s the video that convinced me to seek out Stenocereus (queretaroensis is depicted, though they don’t mention that):
https://youtu.be/g1s1RhnrIfMWith an additional (Spanish) video showing an orchard that grows several species of Stenocereus for commercial production:
https://youtu.be/RQ9UlZYJq3cHere’s the thread on Fruiting Epiphyllums:
https://tropicalfruitforum.com/index.php?topic=15813.0;allHere’s an article that mentions several named prickly pear fruiting cultivars (among other cacti), but I haven’t found any of them (most net searches lead me to believe that practically any random opuntia can prolifically bear tasty fruit, though I don’t know about that):
http://jamesenterprisesoftexas.com/pear.htmI myself have an unnamed spineless Opuntia, three Bilberry Cacti, several unnamed Dragonfruit (and some Palora yellow megalanthus), Argus and Padre Epiphyllum (I can’t find “Daybreak” or “Fern La Borde”). All are still small.
Note: even spineless Opuntias have glochids. Handle with care.
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I also tried to grow another succulent, Carpobrotus glaucescens, a few years back, as the fruit is said to be quite good. But despite being advertised in almost weed-like terms, it failed to thrive once it hit adulthood. The dryness hurt it, water hurt it more, the sun hurt it even more, and the shade seems to have been worse. I haven’t the foggiest idea what went wrong that time... but if there’s a chance at success, I’d like to try again. I got my seeds from Fair Dinkum Seeds, and shipping used to be cheap, but I don’t know if that continues to be the case.
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Edit: Mammillaria fruit seems to be a popular forage in Zacatecas, Mexico. Not sure on the species though. The fruit is called “Chilitos” (little chiles).