I think that a good economist is a someone who has profound insights into how human economy works. Someone who really understand the mechanism of economy. Whoelse can be? Creativity in modeling seems a key to be a good economist. Ability in econometric analysis? It is necessary, but it does not provide any insight.
In history, without any doubt Keynes is the best economist. Among current economists, I admire Paul Krugman because of his insights and his participation in social issues. I would like to hear what you think.