The reincarnation theory is crap.
ignoring all the holes in it (how could the 4th ask the 3rd to treat Naruto as a hero if Naruto wasn't created yet?), the main reason why it's wrong is becuase it goes against the "underdog" theme of the story..
If Naruto is the forth hokage, then it means that his entire race to being hokage was decided at birth, and that makes fools of the fans...

the father\son theory has enough holes of its own, but they can be solved and add deapth to the plot at the same time, the reincarnation theory can't be...