Kind of depends on the situation. The compliment I'd want most is vastly different coming from a boss or coworker, or a child, my parents, a friend or a lover.

But in general something tied to reality works best, when I've done something recently that ties into the praise. That goes both for practical stuff like how creatively or well I did a work task or built a table, and more personal/interpersonal stuff like how kind or insightful I've been when listening and giving advice to a troubled friend.