In Private Transfer you can/coach also choose to do sightseeing by private vehicle which will be available from one point to another. The private vehicle will be pre-booked on a pre-decided route and timings decided in advance as well.
Vehicle at disposal means that a car will be with you throughout the travel trip for which timings and kilometers will be decided in advance. If you use the car outside the travel package distance or time limit then it may not be possible or it will charged additionally. Vehicle at disposal offers more flexibility and control over the itinerary. Also private van tours include a coach at service.
SIC (Seat in coach basis) SIC coach transfers depart only at fixed times and stop at different hotels enroute where other passengers may be picked up or dropped off which mean it time consuming. You will be traveling with other passengers and passengers of different nationalities which offers a good chance to interact with people from different parts of the world. Before joining the tour you need to exchange tour vouchers for your original tickets from the concerned office. Many time the tour starting point is not from the hotel so then you need to reach the departure point from your hotel at your own expense.