Prioritize the Musée d’Orsay if this is your first Paris trip, if you care about 19th-century painting, or if you want one museum that delivers a very strong concentration of Monet, Renoir, Degas, Manet and Van Gogh in 2–3 focused hours.
The setting matters almost as much as the collection: the former station hall gives the visit real character, and starting on the 5th floor works well because the most popular Impressionist rooms fill up fastest; practical details are straightforward too, with tickets from €16, address at 1 Rue de la Légion d'Honneur, and easy access from Solférino or Musée d’Orsay on RER C.