Depends on the child. A big boat gives them space to move, which helps, but the crossing drags and bored children get restless. Check the age rules on the tour and judge your own kid rather than following a blanket rule.
The speedboat. Less time crossing means more time at the stops, and on a full-day trip that gap is noticeable.
Usually still the budget big boat. Add the optional kayak and any park fee collected separately before you commit to that, though.
