They both look stranger in motion, but I guess it depends on the individual viewer, or how far you’re willing to suspend your disbelief. Although I personally aren’t a fan of this technique, it was convincing enough to not take me out of the movie. However I wouldn’t say that it looked “real”, but it was quite impressively done none-the-less.

And although a look-alike actor would have been more “normal” looking, I must admit that more-or-less seeing Cushing and a young Carrie Fisher made the experience quite interesting. I’m at least glad that they didn’t CG Mon Mothma as she has far more scenes.