Depends on how much production I can throw at the city, to move it in a low amount of turns.
I always plan to move a aquatic city some, to cover it's effective area and grab any close by strategic resources, even if they end up outside range of the final location of the AC.
Playing on sparse maps, I find myself with extreme shortage of resources, placing towns like crazy and waiting for them to grow, doesn't seem as efficient as hunting resources with a sea town, so I often put down a water town with the single purpose of painting the map, so I get strategic resources inside my border, with a small army of workers capturing the strategic resources, while the city work on grabbing more.