I got Mirena 8 weeks post baby. I had cramping (I was warned by gyn to take ibuprofen about 30-45 mins before appt), but it was not too terrible, certainly not on par with LABOR. For about three months, I would spot irregularly and only a small bit. I have had about 7 total periods in 3 years, but these are very light and panty liner tops. I usually get a period when I return from my summer off (am a teacher) and become confined with my department of AMAZING female teachers (Science). It seems by the third month back, everyone is sync'd. Kind of funny in a way. My gyn will NOT give Mirena to a single, non-mom woman. She says there is a risk of uterine puncture which may leave the woman without an opportunity to have a baby.
I used Depo for about a year and had to stop. It was terrible. I gained weight, mostly water, had horrible mood swing, and finally had a 3 month light period without break. This was not a good choice for me. However, it was an excellent choice for my friend who had none of these conditions and recommended it to me. I think it is more about the person. I tried to love it as I can not take estrogen (I am a clotter) but progesterone is an option.