Hmmm, this is a great question because I think the compliments we struggle to accept are the ones that touch on the things we are most sensitive about or disbelieve the most in ourselves.  I really struggle with being told I am pretty.  I don't hear it often and when I do I tend to dismiss it completely or if it's a man I tend to believe it has ulterior motives and I really struggle to believe it.  I remember getting up the courage to do some Boudoir photos done au natural and there was a questionnaire first, on it was basically this question and I answered the same as today.  In the middle of shooting she stopped and said "I can't believe you think you aren't pretty, you are stunning the camera is loving you."  in the moment I managed to run with it but I never truly believed her.  I need to start telling myself I am beautiful, I'll never believe someone else if I don't believe myself.