Well, you're not hiking with them, so take them all. Aim to record the experience of the day, rather than just trying for that award-winning whale shot. You might get lucky, but they're pretty hard to shoot. I'd choose a sunrise/sunset trip for the best chance of interesting lighting that can make an otherwise dull shot of a whale's back more interesting. Consider polarising filters, too. The mist from a blowhole can generate a rainbow, and the polarising filter will intensify those colours. Polarising filters can help with several other aspects of marine photography. Darker blue skies, turquoise water, better cloud definition, less glare from the water. You also have a chance of getting a half-decent shot of a submerged whale is you are lucky enough that one swims under the boat.