Clinton's wild card would be Sen. Mark Pryor. provided he wins re-election. He's a friend, he could bring Arkansas back into the fold, and he'd be loyal. Hillary has never been personally popular in Arkansas. She's not Southern, and she is considered to be one of the reasons Clinton lost re-election in 1980.
Take it from a Democrat -- Pryor is too conservative to be Hillary's running mate. The base would revolt.
They would not revolt. There'd be some grumbling, then in a few weeks everyone would be back to only caring about beating the (R).
Now, Christie/Martinez on the other hand, would have solid potential for a third party Tea Party candidate.
You really think a pro-life, anti-gun control, anti-LGBT rights senator with a poor environmental record is going to pass muster with the base? Do you realize how many constituencies within the party would be hugely pissed off?
And what will the base do? Vote Nader? The Democratic base tends to take whatever is given to them. Just an example: the base enthusiastically supports the Heritage Foundation's/Bob Dole's/Mitt Romney's healthcare plan.
It wouldn't be Nader this time, but as someone who was around for and voted in the 2000 election, we should not tempt fate. And the base won't take just anything -- note the recent torpedoing of Larry Summers. You do not consolidate your base by putting a candidate on a national ticket who disagrees with large swaths of the party platform. Just Pryor's pro-life position alone is a deal-breaker. There is a reason why there has not been a pro-life Democrat on a national ticket in over 20 years -- it is a litmus test.
Democrats have been taking liberals for granted way too much. We will make sure to jump ship if Clinton chooses someone even more right-wing than herself.