The city has a strong visual identity, yet a useful stay is usually shaped less by what it looks like than by what the day is for. A visitor at a trade fair, a couple on a short break and a group joining a cruise are not solving the same Barcelona.
Before booking around a broad “city centre” idea, decide whether the practical centre is Eixample, the old city, the waterfront, Fira Gran Via or a transport link at Sants.