Favorites are paintings of Franz Kline and Mark Rothko. Difficult to just pick one... From Rothko I like those with more toned down hues. Also Rembrandt and his play with light and shadow and his amazing attention to details. His works are beautiful. Finnish painters, Albert Edelfelt and Helene Schjerfbeck have also been important to me. From sculpt, Auguste Rodin with collaboration with Camille Claudel.
From photography, Vivian Maier, Ernst Haas and Saul Leiter. Especially their more unconventional works.
If I was forced to choose one, then maybe this from Rothko: