Difference between copper IUD and the mirena??

Ok so I'm 4 months postpartum and I'm thinking about getting on anIUD but I don't know which one, the copper or the Mirena! Is there a huge difference between the 2? I know the mirena has hormones and the cooper one doesn't but I need more info! Which one would u recommend? 
Can I trust them 100%?
Will my partner feel the strings during sex? 
Is there a possibility of it coming out on its own? 
Will my period be the same? 
Pros and cons, I need as much information as I can get so drop a comment below!!  Thanks in advance :)