A lot depends on the helicopter you want to fly.
A stable coaxial helicopter will be a lot easier to control (with a human or by a computer).
I think quadcopters are a lot easier for computers to control than collective pitch helicopters.
I think there may be some autonomous collective pitch helicopters now a days but helicopters can be very difficult to control and it's far from a trivial task to make one autonomous.
What sort of helicopter were you wanting to use? It would be a good idea if you were able to fly the helicopter yourself prior to attempting to get the helicopter to fly autonomously.