Shade is first, and it is not close. A Maltese July afternoon at anchor without a sun top, a bimini or a flybridge overhang is genuinely unpleasant by two o'clock, and no amount of hull styling compensates. When guests tell us the charter was too hot, it is almost always a shade problem rather than a yacht problem.
Second is the bathing platform. How you get in and out of the water determines how much swimming actually happens. A hydraulic platform on the Manhattan 66 or the Sunseeker 86 turns the sea into an extension of the deck; a vertical ladder on a smaller boat is fine for adults and hard work for a seven-year-old or a grandparent.
Third is interior refuge. On a day charter you do not need cabins to sleep in, but you very often need somewhere cool, dark and quiet — for a nap, a feed, a phone call or a headache. Air conditioning running on the generator at anchor is the difference between a family lasting eight hours and asking to come home at five.
Fourth is speed, which matters less than people assume but is decisive on two routes: a half-day run to Comino, and any day where you want both Gozo's west coast and a Comino swim. The Axopar 45's three engines buy you an extra anchorage; on the larger yachts you trade that for shade and space.
Fifth is crew, and it is the quietest variable. A skipper who knows which bay is sheltered in a north-easterly, which pontoon jams with cruise traffic and how to talk to children will lift an ordinary yacht above a better one crewed indifferently. We choose the crew as deliberately as the hull.