Mirena vs. Paraguard

I've recently been thinking about switching to an IUD so I don't have to worry about taking a pill every day. After reading up on the two, I understand the normal differences (length of time, hormones/no hormones, periods, etc). What I'm not understanding is that in the pamphlet about Paraguard, it said your partner can't feel it and in the Mirena, they might. How is this so if they both have strings? What are your thoughts / experiences with either??