Zanzibar is small on the map and surprisingly varied on the ground. Where you stay decides what kind of week you have, and the coasts are different enough that people who loved one can dislike the other.
The north: Nungwi and Kendwa
The one part of the island where the tide matters least: you can swim at any hour. Sunsets over the water, a busy beach life, restaurants and bars within walking distance. If you want ease and some evening energy, it is the simplest choice.
The east coast: Paje, Jambiani, Matemwe
The postcard side. White sand, turquoise water, and a tide that walks out hundreds of metres twice a day, leaving flats where seaweed farmers work and kitesurfers wait for the water to return. Quieter, more villagey, and the light in the morning is extraordinary. You plan swims around the tide, and either that charms you or it does not.
Stone Town
Not a beach stop but a real old city: carved doors, narrow streets, the night market, and a history that runs through spices and the sultanate to the slave trade, which the old market memorial addresses without flinching. One or two nights at the start of your stay is the right dose for most people.
The south and the smaller corners
Quieter still, with mangroves, lagoons and a slower pace. Good for second visits and for people whose ideal beach has nobody on it.
The short version
Swim-any-time and social: north. Postcard views, kites and calm: east. History and street life: Stone Town first, then either coast. Tell us which paragraph sounded like you, and that is where we will start.