It is rather difficult to highlight one. I can name just some of them. Hieronymus Bosch, Claude Monet, Konstantin Korovin, Isaac Levitan, Mikhail Vrubel are the names which come first to my mind.
As for me, I don't like to watch painting in museums. Big classical museums make art dead. This is especially true for painting from Impressionism to modern art. Art lives in a special atmosphere in other cases we have some sort of canned goods.