Can't I'm much of an expert on them but prickly pear/opuntia/nopal seems to be quite a large family of cactus. Many grow wild around here but edibility varies. I think usually "prickly pear" refers to the ones that provide the edible fruits but may not have palatable "pads". There are several different varieties and colors that you can even buy in bags, pealed and prepared to eat right out of the bag. Nopal is used for the ones with edible pads which may not have good fruit.
Nopales are abundant in grocery stores here and our journeys sometimes take us past sizeable fields of cultivated nopal. The stores bulk buy the nopal pads and have someone use a sharp knife to shave off the glochid-loaded areoles. You can dice them, blanch them and use them in salads, use them as a vegetable, juice them or grill them in the barbecue. They taste a little bland to me but the barbecue really seems to bring out a delicious flavour although it also turns the juice into a clear slimy goo that doesn't look too appetizing. Just oil and salt them then sear. The best nopal for eating seem to be the younger, thinner pads and cultivating the store bought pads (grabbed before the areoles were removed) produces plants with thinner pads than other varieties. The few types of nopal I have tried grow really fast if they are watered. A single rootless pad poked in the ground will multiply to 10 pads within a year in my sunny, hot climate with winters that rival summers in more northern climes.
I've never tried dragon fruit (hylocereus) but there are several varieties and colors (https://www.amazon.com/Dragon-Edible-Hylocereus-Undatus-Fragrant/dp/B00TQDJVH0
). Pitayas (stenocereus) grow wild here too. The ones I've tasted were quite juicy with a texture and flavor like cucumber. They weren't overly sweet and also had a hint of lemon. They contain a lot of rock-hard seeds. I always felt the name was inspired by the sound of spitting out the pits. Native Indians dried these pits and ground them into a flour. There are different wild varieties. One sweet one (pitaya dulce) is s. thurberi, commonly known as the organ pipe cactus. The fruit is red. A sour edible one (pitaya agria) is s. gummosus. I haven't tried it but it was a staple to natives in the region and is said to taste quite pleasant.
Pachycereus, such as the giant cardon (p. Pringles) also have edible "pitayas" which are reputed to be sour and perhaps more of a "survival" food although the pits were used to make flour.