The Philco and Magnavox units are mostly identical. The Magnavox has a power switch. The cases are different colors (Philco is white, Mx is black).
These two do not seem to have the low-audio/intercarrier-buzz problem that the Zenith/Insignia units have. I think the Digitalstream also has low audio, not quite as bad, but bad enough. These two have good audio. Also they pass-thru the antenna feed when not in use. Only drawback is the remotes aren't programmable for the TV, and they do not adjust volume internally (you have to use the TV set's remote for those functions -- not an issue on a '40s roundie though!).
So for your new set, for general use, the Zenith/Insignia is best. The menus are cool, the remotes program, and the boxes have internal volume control.
For your ancient roundies, Magnavox/Philco is the way to go.
I still don't have an RCA, so the jury's still out on that one. Anybody having low-audio/buzz problems with it? What are its pros and cons?