Generally, A, B of course has its place and time but I'd prefer to be in and out and down. Whenever I do my rest-pause style training, I train to failure every set, I train until I'm absolutely sure that even if I rest for another minute I couldn't do a single rep. I couldn't imagine how long I'd spend in the gym if I had to do 30 sets but yet I still see results anyways.
Now in terms of other HIIT techniques, I really only prefer rest pause. I know if I do a drop set immediately I could get a pump, or I could literally kill the muscle with forced reps (via Demon Training). But this doesn't seem natural to me, I like to work out frequently on full body routines so I'd prefer to just stick to what my bodies capable of on it's own.