Radio talk shows are usually not that bad, mainly because most of the people who call in are not professional talkers and the host is, so he can usually keep them from running away.
Still, incoherent callers are seldom any great improvement over slick and slippery ones. You don't learn much from either.
What you learn from radio talk shows depends on how wide and how deep the knowledge of the talk show host is. Some of them -- Rush Limbaugh, Sean Hannity, G. Gordon Liddy and others -- are right on top of things.
The only problem is when they allow some hyped caller to just ramble on and on. That is when it is time to turn to some FM music station, preferably one playing soothing music.
The best part of a radio talk show is usually a monologue by a well-informed host. Rush Limbaugh often lets a caller's comment or question serve simply as a point of departure for giving an explanation of his own about some issue of the day.
Sometimes a well-informed and articulate guest like Condoleezza Rice or Alan Greenspan can provide some real insights to both the hosts and the audience. But these are the exceptions.
Usually the best roundtable programs on television are about sports. Probably that is because there are no predetermined positions or prepackaged partisan talking points.