This pdf from crfg is obviously useful for those people thinking about loquat varieties. Don't take it too much as gospel, since it's NorCal specific and maybe touting some varieties. The part about which varieties bear well was interesting. Loquats are fairly narrow in how good they can be and how different they can be from one another. Also, keep in mind that one may strongly prefer *seedling* loquats as compared to commercial varieties because they typically have less thick skin than what commercial breeders have been seeking. Same game as Blemheim apricots. Seedlings of white loquats are more likely to be sweet. Orange loquats are more likely to be a bit more robust. Anyways, much like with feijoa or pawpaw varieties, people tend to tout varieties that just don't made much of a difference from norms. However, I think, like figs and unlike feijoas or pawpaws, loquats have been bred for so long that the best has been gotten out of its germnoplasm by now, mostly.
http://www.crfg.org/chapters/santa_clara/FruitLeaf/SepOct09.pdf