It’s pretty hard to argue the Mona Lisa isn’t the most famous painting. I’m not necessarily saying the best or most technical (or whatever art terms you want to use).
My brother-in-law saw the Mona Lisa in the Lourve, noting it wasn’t much bigger than a postage stamp, behind bulletproof glass, and battling a large crowd to get to it. I retorted that I saw what I considered #2: Van Gogh’s Starry Night by walking right up to it at MOMA.
What would be #2, if not Starry Night?
Monet’s Water Lilies
Botticelli’s Birth of Venus
Seurat’s La Grande Jatte
Leonardo’s Last Supper
Michelangelo’s Creation of Adam
Rafael’s School of Athens
Donatello’s ____ (what did that turtle do?)
Granted, there are others, like American Gothic, Klimt’s Kiss, and Guernica (is that Picasso’s most famous), but I wouldn’t say they’re #2.