I'm on my second month with Mirena, and so far so good. I just saw my ob/gyn yesterday, and it's perfectly positioned. The uterus is healing well, and the pain I was experiencing the first month is going away. I was on Depo Provera for 8 years prior to Mirena, which has the same hormone in a higher dosage. No complaints for Depo either. I stopped the Depo because of the length of time I was on it. It took about 9 months for my period to return after stopping the Depo.
My IUD was also inserted by a ob/gyn who was 57, and performed her first appendectomy at the age of 20. She was very experienced. Which is what I recommend first and foremost, an experienced doctor to put it in.
What I didn't like was the NuvaRing. That made my feel so weird and dizzy. It also caused irritation inside of me, and on him too (all that rubbing! ;)