Unlike almost every other citrus variety, you eat the entire fruit, skin and all. What's more, the sweet part is the peel, whereas the pulp is extremely tart (or at least sour enough that the peel seems sweet in contrast). When you eat a kumquat, you find yourself nibbling, squirrel-like, around the outside of the fruit, discarding the center. That's not necessary with the Meiwa variety. Its pulp is much sweeter than most kumquats.
For this reason, the variety has long been considered the best for eating out of hand. (An alternate name is the Sweet Kinkan, which sounds like something out of "The Mikado.") You can spot Meiwas because they are nearly round and most other commercially available kumquats are oblong.
How to choose: Kumquats should be deeply colored and firm. Pass by any that have soft spots.
How to store: Refrigerate kumquats in a tightly sealed plastic bag.
How to prepare: If you're not going to eat them out of hand, slice kumquats thin and add them to a winter salad.