Geass is awesome. It would allow such scenarios as the one above lol. However they often have requirements and would be useless against things such as robots. Hiei's jagan eye is probably a better doujutsu as it allows mind control of humans and even weaker demons and supernatural beings, without limit and gives him extra sensory abilities as well as superior physical abilities. That would probably be my doujutsu of choice. My overall pick though would probably be the power of a super saiyan. Reality warping is kinda hax and almost too much. I would only pick that if someone else had a similar power. Really though there are so many I would pick as easily as ssj power.