I think if you want to get as close as you can to O Sensei's aikido you have to train in the Iwama tradition. M. Saito was with O'Sensei for 23 years and trained with him outside of standard class times. I know this will anger a lot of people but that is just the way it is. Whether or not that is good or bad, I do not know. Personally I have a strong background in Iwama style but I also do not think that I can't learn from other styles of aikido and even koryu.
I always found it interesting when these shihan would claim to be uchi deshi for O'Sensei after the war and did not spend any time in Iwama.
That is simply your opinion, not supported by fact. Mr. Pranin did speak highly of the Saito Sensei's attempts to preserve what he saw and learned from O'Sensei, but also stated that his Aikido was not O'Sensei's Aikido. There is the external form of the waza and then there is what is hidden inside. Saito Sensei did not appear to fully get what was inside either. Instead of trying to say that one is better than another, it seems more important to try and piece together what the various direct students did get from him.