There is no universally better option here, only a better fit. The question is really about how much you want to be in charge.
A group departure is cheaper per person, because the airfare, coach and guide are shared. It is also considerably less work: someone else has already decided the route, booked the hotels and solved the connections, and a tour manager from Colombo travels with you. For a first trip to a country where you don't speak the language, that is worth a great deal.
The cost is flexibility. You move at the group's pace, you eat when the group eats, and you cannot linger at the museum you liked.
A private tour reverses all of that. Your own vehicle and guide, your own dates, your own start times, at a meaningfully higher price per head, unless you are travelling as a party of six or more, at which point the gap narrows sharply.
Our rough rule: first time abroad, or travelling solo, take the group. Travelling with an extended family, on a honeymoon, or returning to a country you already know, go private.
