I agree, it's hard tp pick between them.
My suggestion to help pick are based on intangibles.
1) Have you sailed on either ship before? You can choose to ride the same ship again, or choose to ride another.
2) Pick the ship with the departure and arrival day that best fits your schedule.
3) Itineraries are slightly different, even with the same ship. Pick the itinerary that you like best.
4) Why choose between them? Ride both, first on the ship with a Saturday departure, then on the second with a Sunday departure. Turn that one week cruise into a two week cruise on two ships.