Color gets all the attention, but sheen decides how a room actually looks and holds up. The shinier the paint, the easier it is to clean and the more it shows imperfections in the wall.
Flat paint hides dents and patches best, which makes it good for ceilings and low-traffic rooms. Eggshell has a soft glow and wipes clean, so it's the most common choice for living rooms, bedrooms, and hallways.
Satin stands up better to moisture and scrubbing, which works well in kitchens, bathrooms, and kids' rooms. Semi-gloss is the standard for trim, doors, and baseboards, where scuffs and fingerprints happen most.
Whatever sheen you choose, the wall needs to be patched and sanded smooth first. Shinier paint makes every flaw underneath easier to see.