The best compliment you can give to somebody, is a compliment that will allow her/him to improve as a person, and not stay self-satisfied.
With my students, for instance, I try to show them the positive qualities of their researches, where they are talented and why...
It doesn't mean I won't mention their weak points, it means I try to help them to develop the better part inside them.
Let's talk like an NF: What I'm trying to do, is to send them good karma.
In this mad world full of stress, anger and bitterness, a good karma is always useful.