I think that's a very difficult question because our impression of life, along with our artistic preferences, changes as we grow older. It can sometimes change on a daily basis.
Although I can't give a definitive and exact answer, one artwork with a lasting effect on me is Nighthawks by Edward Hopper (oil on canvas, 1941).
To me, the diner is both an extension of, and sanctuary to, the dark silent street outside. The contrast between the shadowy, deserted street and the well-lit peopled diner is eroded by the lonesome quality that pervades throughout the whole composition.
There is a "ships that pass in the night" feeling about this painting. No matter where you are, or at what time of day, there is always new conversation and interaction to be found, if only fleeting. I think that's what I love about it although it can sometimes leave me feeling a little cold.