What flooring adds the most value to a house?

Real wood, consistently. Solid or engineered hardwood on the main floor, ideally running continuously through the connected living space, reads to buyers as a permanent finish rather than a surface. Refinishing existing hardwood is often the strongest return of all, because the cost is a fraction of replacement and the result reads as new. Beyond the material itself, consistency adds value: one floor flowing through the main level looks more expensive than three good floors meeting at thresholds.