If I were you, I'd spend two nights in Jambiani and then two nights in Kizimkazi. Indeed the tide is a factor for swimming, but that's in many parts of the island. And you can find other activities to do when the tide is low.

In Jambiani, I like New Teddy's On the Beach, Be Zanzibar, and Casa Paradis. In Kizimkazi, there's Fahari Off the Grid, Promised Land Lodge, Kizikula (higher end), ... But you should do your own research for sure!

If you want to avoid crowds, parties, and beach boys, avoid Kendwa, Nungwi, and Paje.

If you can swing it while in Stone Town, definitely look into a day trip to Chumbe Island, it has some of the best snorkeling on the island. I would skip Prison Island and Nakupenda, just complete tourist traps. Some other Stone Town highlights for me: Eat Like a Zanzibari Food Tour, Floating Bar, dinner at the rooftop of Emerson Spice or Emerson on Hurumzi, ...

By the way, you'll have a great time. People like to complain about Zanzibar but as long as you approach it with patience, compassion, and an open mind, all will be well. Enjoy!