Gynecologist thinks mirena is best for my pcos and prevention of endometrial polyp.. endocrinologist says combination bc is better & mirena not good??

Both are reasonable: Both are reasonable options with advantages. Mirena is highly effective and does not require daily maintainence for up to 5 years. Most have light or no menstrual cycles which is a nice benefit. Theoretically but unproven the Progesterone could suppress endometrial polyps but polyps are rare at age 20. Birth control pills would regulate your cycles. Neither will “fix” PCOS.