Ditto about the Implanon, it's not recommended for anyone with a history of depression which I found out the hard way. No personal experience with Mirena, beyond knowing that they work differently - Implanon is supposed to stop you ovulating, where Mirena won't allow a fertilised egg to stick. Not sure if that makes a difference to you, but for me being pro-life and a JW, its a BIG difference

Hope that's some kind of help for you