D.D.
I have Mirena, and I love it. No, I don't have mood swings. And I have not gained weight. And, bonus, I don't get my period anymore!
The only downside I had was that I was told that it's common to have spotting for up to 3 months after it goes in. I had spotting for 5 months, very light, but annoying - I was also postpartum when I had it put in, and I don't know if that made a difference. But once I got past the annoying spotting, it's been great.
I've had mind for more than 3 years, and when I'm at 5 years, I'll get it replaced with the same thing.