For one or two people travelling light, the scheduled catamaran is cheaper, and there is no argument to be had about it. The catch is that it runs to a timetable, sells out in summer, and drops you at a port rather than at your door.
A private boat is priced per boat, so the arithmetic flips as the group grows. Six or more people crossing to Split, and the price per head lands close to catamaran tickets, with your own departure time, your luggage on board and no queue at either end. Twelve people and it is usually the cheaper option outright.
The other difference is what happens when a plan changes. A missed catamaran means waiting for the next one; a private transfer moves with a message. If the sea is genuinely too rough, we move the transfer earlier, later or to the next day, and if nothing works any prepayment comes back in full.
Solo or a couplecatamaran is cheaper, if it fits your timetable
From six peopleprivate boat is close per head, door to door
Twelve peopleprivate boat usually cheaper outright
Luggagefree on a private boat, no ferry queue