Manning's actually a good pro-QB, well-matched with his particular team--when they're healthy (at receiver, of course, which they HAVEN'T been--but also at RB, to take the pressure off the must-pass situations).
I wouldn't vote for Newton for ANYTHING, just on principle--the fact that you are right about his limitations and propensity for errors (unlike Manning's INTs, Cam's tend to be unforced, born of an arrogant faith in skills he doesn't really possess) makes this all the easier and more correct.