You can visit the Galapagos any time of the year as there is always something wonderful happening in the Islands, especially with wildlife’s behavior and natural events.
From mid-June to early-December you have a mixture of warm and rain (afternoon showers), and Ocean waters are warmer and calmer due to the “El Niño” current. From mid-December to early-June is the cool/dry season on land and Ocean, especially because of the passing of the “Humboldt” current through the Archipelago.
Taking a Galapagos cruise is considered the best way to explorer the Galapagos as it gives you the opportunity to reach the remotest islands as you sail at night from site to site, which means more time to enjoy the location and day’s activities.
However, if you are susceptible to sea sickness the feasible alternative is taking a nice land-based tour with hotel accommodation on the populated Islands of Santa Cruz, San Cristobal and/or Isabela; from here you can enjoy interesting day-tours to the nearby sites or Islands; you will also have the possibility to enjoy snorkeling and other activities while taking day-tours.