I have had some very good fruit from Opuntia ficus-indica, my favorites are the green ones (here they are called "bianche" which means white). They are both very sweet and crunchy. Hard to beat when chilled, in my humble opinion, during an hot day in august. I know that the numerous seeds are disliked by many peoples, but the taste alone, is, in my opinion, very good.
I haven't tasted many cactus fruit, aside from these, but the cactus family has usually very small seeds, so, excluded the pricky pears, they shouldn't be a problem.
Cactus anyway have some great advantages. At least in the south of italy they are effortless to grow (literally effortless). They don't need water. You can plant them in any arid soil and forget about them all year long, except for picking the fruits. And are easy to reproduce - very easy. They ship well.
Well, yes, i'm with you adam, i think they deserve to be grown more, at least in places with water shortage.