What is the best top coat to protect paint?

Best top coat to protect paint depends on surface being protected. For interior house walls, best top coat to protect paint is high quality 100 percent acrylic latex paint itself in satin or semi-gloss finish, as it is washable and durable, but if you want extra protection over wall paint, you can use clear acrylic sealer or polycrylic for high traffic areas, though not commonly needed. For interior wood trim, cabinets, and furniture painted with latex paint, best top coat to protect paint is water based polyurethane like Minwax Polycrylic or General Finishes High Performance Top Coat, which provides hard clear protection without yellowing. For exterior painted wood, best is exterior spar urethane or marine varnish with UV protection. For floors, best is oil based or water based floor polyurethane like Bona Traffic HD. For cars, best top coat to protect paint is 2K urethane clear coat with hardener, plus ceramic coating or paint protection film for extra protection. For art and crafts, best is clear acrylic sealer spray. For nails, best top coat to protect color is gel top coat or long wear top coat like Seche Vite. So for painted wood, polyurethane is best protective top coat, for walls, quality paint itself is protection, for cars, clear coat plus ceramic coating is best.