I don't have an all time favourite. It all depends on mood and circumstance. But lately I have been enjoying "The Mamas and the Papas" (Egad am I ever old!) Even their melancholy songs are so beautiful they are cheerful somehow. And then again, their brilliant harmonies on even the happy songs can make me cry.
My favourite classical composer is Mahler. He can destroy the universe with a thundering crash and then tenderly build a new one. Why is it that I can relate to that?