I had both. Paraguard pre-pregnancy, Mirena post-pregnancy.
The Paraguard caused me mild cramping for the first 3 months or so. (Remember, I hadn't been pregnant ever when I got it.) After that, it was fine until about three years in. For the last several months that I had it, I had helacious periods. Super heavy, lots of cramping, etc.
After DD's birth, I got the Mirena. It did make me break out for the first several weeks. I had it for about a year. I got it out because I was starting to feel like I was about to get my period all.the.time. yet I never got it. Also, I suspect that it was part of the reason I have been having SUCH an impossible time losing baby weight.
If I had to do it again, I'd get the Paraguard, FWIW.
Trying to turn hearts and minds toward universal healthcare, one post at a time.