Choose sweet potatoes with tight, unwrinkled skins without any bruises or blemishes. Bigger, however, is not always better; larger sweet potatoes are starchier. So, look small- to medium-sized sweet potatoes.
Unfortunately, sweet potatoes generally do not store well and once they start to spoil, they rot quickly. Even if you think you can cut away the spoiled parts of a sweet potato, it negatively affects the taste of the entire potato.