"Believers of Christ" is true, but incomplete, since Christians are "acceptors of Christ," unlike the demons who also believe. "God's child" is a good one, since all throughout scripture, only God's followers have been called his children (and if you follow, then you've accepted him, and if you've accepted him, you believe in him). "Saved sinners," and "Forgiven" are basically the same thing (if you're forgiven, you're saved. If you're saved, you're forgiven). "Christ-like," "Jesus' Disciples," and "little Christ" imply following Christ, which is nearly identical to "God's child."
I put "forgiven," though, since that specifically sums both belief and acceptance of Christ.