Bottom line: choose Barcelona for Gaudí's colourful architecture, Mediterranean beaches and a relaxed pace; choose Madrid to dive deep into Spanish art, history and tradition. Barcelona is a coastal Mediterranean city — its icons are Gaudí's Sagrada Família and Park Güell, and you can walk from the Sagrada Família to the waterfront in a single day; the Gothic Quarter and El Born offer strong café culture. Madrid shines with grand plazas, top-tier museums (the Prado–Reina Sofía–Thyssen 'art triangle') and a more traditional, fast-paced Spanish atmosphere — great for nightlife, cultural events and top tapas bars. If you only have a day or two, Madrid is easier to cover; the two cities are about 2.5–3 hours apart by high-speed AVE train.