New update.
Red: Rubio
Blue: Christie
Green: Walker
Yellow: Bush
Dark Yellow: Paul
Pink: Cruz
White: Tie (Ohio: Christie-Paul. )
If this map is correct, it means that each candidate currently leads in this number of states:
Rand Paul: 9
Chris Christie: 7
Ted Cruz: 2
Jeb Bush: 1
Marco Rubio: 1
Scott Walker: 1
And those states they lead in, are equivalent to this number of citizens (2012 numbers):
Chris Christie: 45.7 million
Ted Cruz: 29 million
Rand Paul: 24.4 million
Jeb Bush: 19.3 million
Scott Walker: 5.7 million
Marco Rubio: 3.1 million (yet it is Iowa, after all)
Appears like Chris Christie is a heavy favourite right now then. With Ted Cruz, Rand Paul and Jeb Bush seeming to be the only ones who can seriously challenge him, unless Marco Rubio really fixes a huge upset for himself in crucial Iowa. 
Also, if Rubio does not run than I could see Bush receiving a majority of the vote that Rubio would have gotten. This could place Bush to first in Iowa and possibly South Carolina.
