Either Barack Obama, or if mid-term there is need, Joe Biden could manage the nation without major mishap or blunder.
McCain is doubtful that way, in terms of temperament and as representing no break from the failed Bush presidency, with which he admits he voted 90% of the time.
For more detail: The NY Times Obama endorsement was extensively excerpted, here, and as excerpted is true in my mind and expresses thoughts I also hold and have independently reached.
Finally, my bottom line, the Palin choice was an insult to the nation and to every sentient voter in it. To selfishly play to a selfish faction of his own party, one he in the past has denounced, and to let them make his choice for him and to uncritically accept the chosen unfit individual, Sarah Palin, as VP running mate says very much about the true character of John McCain, and of what it says, nothing is good. It shows weakness and compromise, not statesmanship, not anywhere near to statesmanship. It is GOP business as usual, and if you liked the last eight years, well --- bless you.
_______UPDATE_______
On the Palin pick, one friend characterized it as, McCain cashed in all of his credibility for a gimmick.