In using shields, I am uncomfortable with both the mirror and transference shields. Both are anthemias to me since it seems that I am choosing between a rifle and a shotgun. Both do the job – one splays bullets everywhere, while the other depends on the ability of the user to hit the target. To me, they can both be dangerous if not properly used.
Because it can pull the energy back into the earth, I prefer using the transference shield. However given my propensity to panic, I would undoubtedly employ the mirror shield since it is easy to dispatch. I need to practice my shielding skills more to ensure a better outcome.
Faced with a person who wants to do me harm, I would use the transference shield. This would do the least harm, even though it does open up other people to be hurt. However, I believe that the person who is trying to get me would need to reassess their target before striking again. By then, other people would have been warned and also have time to protect themselves. However, I do not foresee engaging in some sort of duel. I will do what I can to see that the energy goes into a safe place.
For people who attack unconsciously, I may or may not use the mirror shield. If I want to draw their attention, mirroring would certainly work. It would encourage them to do something. However if they are people who are unfamiliar with magic, then I would use the transference shield, and ground the energy.
As for stopping the person who would deliberately want to do me harm, I would make offerings to Mars Ultor (Mars the Avenger). This is the aspect of Mars, the Roman God of War, who deals with justice and vengeance. As a Roman Pagan, I make offerings to the Gods, request avenging, and make more offerings as a thank you. Roman Pagans as a rule do not practice magic, preferring to ask the Gods to help them instead. Since I am a devotee of Mars (Pater), my offerings are usually welcomed.
I dislike seeing people hurt, therefore I would use the shield with the least harm. For me, that is the transference shield, since I can control the energy. The mirror shield, I would only use in cases of emergencies since it splays energy everywhere.