I can see from all the responses that most women have really liked their Mirena. When I got mine I was very excited also, but then all the side effects kicked in for me.
I was on it for around 8-9 months and in that time I had 3 pregnancy scares because of breast soreness and other symptoms. Although they were just Mirena side effects, it was very stressful to keep thinking I was pregnant. Also, I got migraines when I was on Mirena and had 2 bacterial vaginosis infections (an infection I've never had in my entire life before Mirena and I've tried almost all BC methods).
I don't know much about Paraguard except for the heavier periods, whereas with Mirena your period becomes less and less and for most women will eventually go away. Unfortunately for me, that didn't happen in my case either. I would spot for 2 weeks straight, then normal for 2 weeks, then spot for 2, etc. I felt like I had a light period half the time basically. I also was a bit more emotional and stressed out when I was on the Mirena.
I guess my point is, Mirena has a good reputation and it has obviously worked well for many women, just be aware that it isn't perfect and there are side effects you could possibly get that are no fun at all.
Hope this helps in your decision. I'm on the Depo-Provera shot and it is working great for me, my favorite BC I've used.
Good Luck!
S.