Radio was basically a medium of commentators; John Daly
(yes, of "What's My Line?" fame) is one of the few who tended
not to inject his opinions into his newscasts. Winchell tended
to be on the right, as was Fulton Lewis Jr. on Mutual; two who
skewed left (and one is unfairly forgotten) were Edward R. Murrow
and Elmer Davis; Davis is the one who's unfairly forgotten because
it was he, not Murrow, who first went after Joe McCarthy. The problem
was that he did it on radio, while Murrow did it on the more powerful
medium of television.
And if you go back to the '70s you'd probably say that Eric Sevareid
usually came down on the liberal side, while Howard K. Smith tended
conservative (even though Smith, not Sevareid, was the first to call
for Nixon's resignation in 1974).
The more things change, the more they stay the same.