I will just give my experiences, not my opinion (well, I suppose I won't be able to resist opionion actually!).
I had the mirena coil fitted in May 2006. My dr had been trying to convince me for a long time as condoms caused irritation. She finally convinced me when I was mentally ill, as she said it may help calm my hormones.
The fitting was simple BUT very painful. If you have had a child it won't hurt much; the doctor said it is much less painful than childbirth. I bled for about 2 weeks after, and had bad period pain for the same length of time... really bad! You are supposed to go back and have it checked, but I didn't because I changed GPs for several reasons.
I had gained weight due to mental illness/medication, and the mirena didn't help that cause as initially I had some bloating and that constant urge to eat that you get with your period. After 2 weeks the pain and bleeding more or less stopped and I had no periods until about March this year when I had 2 horrendous days of bleeding and pain and then nothing for another 9 weeks, then a few days of slightly lighter bleeding, then nothing until end of July when I had a seemingly normal period. Time will tell if this is my periods getting back to normal or if I will continue with them every 2 months, but the fact that get lighter and last longer each time, suggests they are settling down a bit.
I did initially get sharp pains down below but the nurse had told me that something like this might happen as the coil settled. But then again you ARE supposed to have it checked out to make sure it hasn't slipped, and they can actually expel themselves, which you may not always notice. The doctor cut the threads off the end of mine so I can't feel them - must get it checked out! Every so often I get those sharp constant pains down there, and it feels like something pushing on my cervix I guess, but it isn't unbearable, just a bit disconcerting at first.
Some people never have periods with mirena, some only light ones and mine were non-existant until recently; now they are light. The main issue for me is the feelings of hunger you get when on your period, seem to be there a lot of the time!
If you want convenience and don't mind initial discomfort/constant bleeding for up to 3 months, then I would recommend the mirena.