Granada and Valencia represent two very different sides of Spain: one a Moorish hill city steeped in medieval history, the other a modern Mediterranean port reinvented around futuristic architecture. Which one fits your trip depends on history versus reinvention.
Granada's La Alhambra and Generalife Gardens are Moorish masterpieces above a medieval old town, with the Albayzín (Albaicín) quarter barely changed in centuries. Valencia mixes eras instead: the Gothic La Lonja de la Seda and medieval Torres de Serranos sit near the ultramodern City of Arts and Sciences, unlike anything in Granada.
Granada's Carrera del Darro and the hillside Albayzín (Albaicín) make for atmospheric, hilly wandering with Alhambra views around nearly every corner. Valencia is flatter and easier on the legs: Ciutat Vella (Old Town) and the bohemian El Carmen (Barrio del Carmen) connect via the Turia Gardens, a sunken riverbed park Granada has no equivalent of.
Granada is one of the last places in Spain where a Tapas Bar Crawl still gets you free tapas with every drink, and a Zambra Flamenco (Sacromonte Caves) show adds a uniquely local flamenco tradition. Valencia is paella's birthplace, so a Paella Cooking Class is the better hands-on food experience, and the Central Market (Mercado Central) is a destination in its own right.
Granada has the Sierra Nevada National Park practically on its doorstep, making mountain scenery and skiing a short drive away. Valencia's nature draw is coastal instead: the Albufera Sunset Boat Tour glides across the lagoon that supplies the region's rice, while L'Oceanogràfic gives Valencia Europe's largest aquarium, something landlocked Granada can't offer.
Choose Granada for Moorish palaces, flamenco caves, and mountains within reach. Choose Valencia for futuristic architecture, a lagoon boat tour, and paella done right. Granada rewards slow, hilly wandering; Valencia suits a flatter, food-and-science-focused city break.