I pick cruises based on price, itinerary, season (warm enough to get in the ocean, if it is part of the itinerary) but not blazing hot. We also aren’t bound by school schedules, so opt for low crowd months (avoiding large numbers of school-age kids, especially free-roaming tweens/ teens).
I would not pick a cruise for holiday theming. I would rather do an additional cruise than pay for a Christmas, Spring Break / Easter or Summer cruise.