I think it makes sense that a little bit of both would do just fine. There's nothing wrong with telling my kid he's smart and cute, because he is.

And I want him to know how special he is and how good looking and intelligent I think he is. But praising the effort sounds great too. I'm sure they love to hear it all. Why not?
If we didn't tell our daughters they were pretty, someone would ask them "Are you pretty?" And they only way they could respond would be "I don't know, but I do a really good job trying to be pretty."
But if you say both, then they know they try really good, and because they try, they are. Right?