Fast answer
Choose Monopoli when the trip wants a coastal base with old-town evenings, beach options, and rail logic that can support nearby coastal movement. Choose Polignano when the specific coastal-town comparison wins the trip. Choose the Valle d'Itria side only when white-town evenings, inland routes, and car-aware planning matter more than sleeping on the coast.
If you only do one thing
For a first Puglia base that combines the sea with easy evenings, Monopoli is a useful default. Use Polignano as the closer coastal comparison, and consider Ostuni, Locorotondo, Martina Franca, and the wider Valle d'Itria separately for inland stays. The dedicated Locorotondo, Martina Franca, and Valle d'Itria guides explain those bases in more detail.
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