This is one of those situations where anyone here should be out, so the discussion is just about minimizing the small chance of not getting out.
With A or D, I think there's a slim chance that I rattle the ball. Either way I have to stroke firmly and I'm trying to juice the cue ball (inside with A, draw/outside with D). With C, I can hit it pocket speed and make the shot every single time no matter how nervous I am.
Also, I think CreeDo's original post is a little misleading:
How do you cinch this ball to guarantee you get straight in on the 8,
and can't possibly miss or get bad shape?
If the goal is to run out just these two balls, I don't need to guarantee straight in shape. All I need is to be straight in
or short of the position line. That will give me a "good enough" shot on the 8 to make it. With C, I know I can get there every single time. With A or D, I have that nagging little bit of uncertainty.
Let me put it this way. If someone gave me 100 tries at this runout using each of the six position routes, and I had to bet on which way I get out the most, I'm betting on C. So that's my answer.