I prefer Hayden Christensen. Technically, it would make more sense for Anakin’s ghost to be played by Sebastian Shaw, for the reasons Hal has already explained. But I prefer Hayden for a matter of nostalgia and because of my great love for the Prequel Trilogy. I mean, seeing Hayden’s face makes me feel a lot of emotions, his face is the absolute representation of what Anakin is to me, and I can’t say the same thing about Sebastian Shaw. Hayden’s face is a face with which we Prequel fans and Anakin fans can identify ourselves with, and see it allows us to feel a lot of emotions that otherwise we wouldn’t be able to experience. So, from a certain point of view Shaw makes more sense, but I prefer Hayden. However, if one day we can find a good version of ghost Hayden that’s closer to his 40s (maybe taking fotage from Kenobi or whatever) then I think we should replace the original version. This way, Anakin’s ghost would be the redeemed Anakin like Shaw, but at the same time he would still be Hayden.