Charles seems to do the most for his country; Felipe seems to do the most in regards to the Hispanic world.
Of course, not taken into account is how much is appreciated. Is Charles really appreciated? His image (responsibility of the media too, in part) is still one of an Edwardian hippy who may not be able to handle the throne. And it is possible to really respect his work in favour of sustainable farming/building and locally grown and organic food, but think he is at his most uneducated when it comes to contemporary architecture.
I do not know if Felipe is appreciated in Spain for reinforcing the ties between that country and Latin America, but he certainly is in Latin America.