I don't think Nintendo would be as successful as they currently without both Iwata AND Miyamoto. It was Iwata that set up the Wii as the console it is and planned Nintendo's strategy however...
- It was Miyamoto who wanted a $100 game console, setting up the Wii as an affordable system.
- Miyamoto who came up with the idea of having Wii Sports, Wii Play, Wii Fit and Wii Music games as the core Wii software.
- Miyamoto who had the idea of a puppy pet simulator that catapulted the DS to huge sales after a slow launch.
I mean out of all the employees at Nintendo it was Miyamoto's idea to have Mario run around sphere's and hence Super Mario Galaxy was Miyamoto's idea. If it wasn't for Miyamoto's game ideas, Wii would certainly not be in the position it is today and the DS may not be either..
So even though I voted Iwata because I have to back my main man up whenever I can :P I still feel that Shigeru Miyamoto is the most important man at Nintendo in ensuring their past, current and future success.