Final answer:
The best candidate for progestin-only pill use among the given options is a woman who is breastfeeding. This type of pill doesn't affect milk supply and is safer for those with a history of blood clots or migraines with aura, as well as being an option for smokers over 35 years old under medical supervision.
Step-by-step explanation:
Among the options given, the best candidate for progestin-only pill use is a woman who is breastfeeding. Progestin-only pills are preferred for breastfeeding women since they do not contain estrogen, which can affect milk supply. Additionally, they are a safer choice for individuals with certain medical conditions.
Women with a history of blood clots are also better candidates for the progestin-only pill compared to combined hormonal contraceptives which increase the risk of blood clots. Progestin-only pills do not increase the risk of thromboembolism, making them a safer option for these individuals. For women who have a history of migraines with aura, using estrogen-containing contraceptives can increase the risk of strokes, hence the progestin-only option is considered safer for them as well.
Women who are over 35 years old and smoke should generally avoid hormonal contraceptives that contain estrogen due to an increased risk of cardiovascular events. However, if a hormonal method is needed, the progestin-only pill may be considered under close medical supervision.