This may be a slightly weird answer to this question, but while I think Emperor's Soul is probably his best-written book, the one I always come back to for rereads is Steelheart. Part of that is probably because up until very recently, I was very busy with schoolwork and less willing to commit to reading longer and more complicated works, but I think there is also something about it that makes me reread it 6+ times and enjoy it every time.