Generally, I strongly support the concept that Schiff did things first and Weisinger stole from him.  See my article "Schiff Came First" here.
http://dccomicsartists.com/vault/Schiff%20came%20first.htm
But  when Schiff's assistant editor George Kashdan was interviewed for Alter Ego he basically disavowed any knowledge of the Martian Manhunter and claimed the whole thing was Weisinger's idea.  It's all still very muddled in my head, but apparently Weisinger edited all the John Jones stories up until 1959 when the Manhunter was revealed to the world and became a regular super-hero.  The writer credits of these early stories are also pretty mixed up because people (like me) have been trying to shoe horn them into the Schiff stable instead of the Weisinger stable.  I currently don't think any of the pre 1959 stories were written by Jack Miller.

I just haven't had the time or energy to go back and read them over again.  Maybe since I don't have anything else to do (government furlough) I might give it a try soon.