I have converted 2 70 Dusters to disc brakes:
Mine; manual with a truck master cylinder
My son's; power with a stock 74 master. It also has rear discs and the residual valve removed.
I prefer manual, but Brendan doesn't like the pedal effort on mine. I think that's because he learned to drive in power equipped vehicles and his daily driver Scion has power. I, on the other hand started driving in a 1959 Rambler, manual drums.
It's really just a matter of personal preference and what you're most comfortable with.
I've had many vehicles over the years equipped both ways and don't really believe that there's any difference in reliability. As long as the cam you choose provides enough vacuum at idle, just go with whichever you and anyone else who will be driving the car, is most comfortable with.