That's a fair question.
Let me give you a rule of thumb. I must emphasize you can't take it _too_ seriously. But it seems to hold quite well that in hard sciences, not just physics, looking from the inside, you notice that the ones who talk to the media are normally the bottom of the barrel. This makes a lot of sense. If your goal is to learn about the fundamental building blocks of the universe, writing blog posts the societal aspects of science doesn't help you with that. Real scientists spend their time doing science. There's very few exceptions to this. In fact right now I can think of a single person who's a world class researcher _and_ a prolific blogger; Terrence Tao, but he's a mathematician.
My point is, you can't judge who's the expert based on the quality of the science produced because you don't have the expertise for that. But believe you me, if someone spends a lot of time doing things other than research, they're probably not the best.