Every single time I've reread either I've found some part of the book that resonates precisely with a situation I'm going through in my life. Even parts I thought didn't apply to me at the time, upon rereading struck a chord.
For example, when I was younger, I identified with Ender but as I've gotten older, I identify more with the adults in the book. Especially now that I have children.
On a side note, the 25th anniversary edition has an introduction that has some gems all of it's own. Notably, there is a line where Card mentions something along the lines of: when I was a child, I never thought of myself as being less of a person than an adult. I just thought of myself as a smaller adult person.
That has always stayed with me since I read it and have always tried to apply that mental model of childhood to any interaction I have with children. It has been particularly impactful now that I have my own children.