Welcome. We usually do a mixture of taking the ship's tours, hiring a private guide and wandering on our own.
We always start off with seeing if the ship's tours are of interest to us. If they are and include all elements we want, we usually sign up for them as they are normally well-run. If the tour doesn't fit our interests, but the area is not good for doing it ourself, we hire an experienced private guide, who is usually someone recommended through this board. If the ship is located in a port with easy access to museums, etc, we speak to the tour desk and ask them to design a walking tour/taxi tour for us.