Kaku is actually a leading scientist in his field, I don't know that Sagan ever was. I think he was more of a "teacher" to the world than a researcher. My high school Astronomy teacher actually loathed Carl Sagan, feeling he dumbed down science too much. I always thought of Sagan as more a philosopher than an astronomer. I never like "Cosmos," I felt it was boring and devoid of true knowledge. I listen to Dr. Kaku's podcast/radio show quite often, he speaks very intelligently and explains concepts quite well.