Liletta is the newest IUD that is similar to Mirena in both dosage and size. It's meant as a cheaper option for women without insurance and lasts up to 3 years (for now).
Mirena lasts for 5 years, releasing progestin which prevents ovulation and thickens the cervical mucus so sperm cannot reach the egg. Some doctors may not recommend Mirena to women who have not given birth as there may be difficulties with insertion related to a narrow cervix.
Paragard is the only copper IUD on the market. It has no hormones but contains a coil of copper which creates a toxic environment for sperm. It lasts up to 12 years and can be used as Emergency Contraceptive.
Skyla is a progestin-only IUD. It contains a lower amount of hormone than Mirena and it lasts up to 3 years. It also has a smaller frame than Mirena so it's suitable to use for women who have not given birth.