This is tough, they're both really good albums. I'm gonna go with Emancipation of Mimi. Songs were a little more fun and memorable for me.
I was 7, so I didn't really appreciate Butterfly when it came out. Then I was 15, and I remember listening to Emancipation of Mimi in high school. Although I've re-listened to them both in recent years, Emancipation of Mimi is still better to me.