So i usually have pretty uncomfortable periods and i was wondering which iud i should get?

Depends: There are basically two type of IUDs (hormone based vs. non-hormone based). Hormone based IUD such as Mirena (levonorgestrel) may be helpful for those with painful/ uncomfortable period as the hormone may lessen your period. Copper based IUD does not have as much of an effect on your period. Speak with your OB/GYN about other hormonal options for contraceptives & menstrual symptoms besides IUD.

Levonorgestrel IUD: The levonorgestrel containing IUD's (Mirena and Skyla in the US) are known for decreasing menstrual flow in most patients and hence decreasing discomfort also during menses. You should talk with your doctor and he/she can explain the different Iuds with you.

See your DOC: Before suggesting you an IUD, other than only uncomfortable period, I need to know more about you such as associated medical conditions, risk factors, life style, future plan regarding family & so forth. I suggest you to see your FP/Internist for full evaluation & methods of birth control. I wish you a good luck