Fast answer
Treat this as an event visit with a specific viewing plan. The cliff-town setting is the attraction, but it does not guarantee access to every terrace or a view from your room.
If you only do one thing
A Polignano stay works when you want the local evening and a walkable return, provided the room entrance remains accessible. Monopoli offers another coastal base but adds a separate journey. Compare the complete return before choosing by room price alone.