I had Mirena, for 2 1/2 years. I had a positive experience with it. My periods slowed/stopped after 3 months. I did have steady weight increase (10 lbs/year) but honestly that might have been poor diet.
I had it removed and 3 months later I was able to conceive with no issues.
Mirena is plastic, therefore less risk of puncturing uterine wall (unlike the copper coil). Low low hormones.
I had some period cramping after having it placed. My uterus was at a bad angle for placement, so my OBgyn had to use a stick to adjust it. It hurt, but was worth the worry free 2 1/2 years I had with it!
That's just my personal experience though. x