After subscribing for over two years to the Nature, Science and Cell podcasts, my preference falls clearly with the former. The Nature podcast is snappy, lively, fun to listen to and has great interviews. The journalists have human voices, sound like real people and manage to confer the excitement of science with a touch of humor.
The Science podcast has several problems, the biggest one is podcaster Robert Frederick. I can not imagine a more unnatural, robotic voice on Earth. Does he speak like that to his friends? Even the text-to-speech voice in my Mac sounds more human that this guy. I also find the usual bit about science policy terribly uninteresting. As in the World Series, this is only concerned with US policy, of course. If listening at night in bed, I am surely asleep by this moment. Both Nature and Science have another feature in common that I think takes unnecessary space, that is the bit on news at the end in which one journalist interviews another. This practice has become very popular in TV talk shows and news programs, and sometimes I can see the point of asking questions to a journalist deeply specialized on a particular topic. But those are not the guys at Nature or Science. I find it totally uninteresting, I much rather have the actual scientists telling the story.