Katia,
Generally I prefer honesty to kindness. However, there are times when kind word don't hurt anything. Also, I don't assume that is true of others. Most people would prefer a compliment to the truth when it comes to their appearance, or their home, things like that, but when it comes to important things like health, what's in their food, they prefer the truth.
So my final answer is, it all depends on the situation. If I had to choose unconditionally, I would choose truth.
Love always,
Elizabeth