Good responses, all. I guess I have to give the final nod to Steve, because you all make good points about him "fitting in" better with the other panelists. Fred did seem a bit ill at ease... he only reluctantly got into television towards the very end of his career. I have some appearances he did on Tallulah Bankhead's "The Big Show" from (I think) 1950 and everybody was making disparaging jokes about the medium of television.
Fred may have actually been funnier than Steve, once you got used to his style of humor, but Steve had that quick wit and smoothness that made him a TV Star (with a capital "S").
I never knew that any episodes of the radio version existed. Those aren't really in wide circulation, I guess. How was the audience informed of the contestant's "line"? A sort of whispered-voice, as in, "The password is..."?
Martin Gabel was fun to have on the show, mainly because Arlene had another area of comedy to mine. Being able to watch these shows every night, most of them for the first time, you are reminded just how funny she was. How astonishingly quick witted and classy these people (all of the main panelists*) were. A while ago they showed an episode with Arlene, Martin, Dick (Kollmar), and Dorothy which had a fun, family dynamic.
*(Except for Hal Block)