I'd give De Blasio an edge. He's tall and relatively media-savvy. Santorum has less of a filter, plus his negatives offset De Blasio's.
If Greg Orman's Senator, he would announce his presidential bid in September.
Given De Blasio's constant response to his administration's scandals being "Shut up and stop talking about it", I think he'd flame out really fast in a Presidential race.
But yeah, the odds are heavy that Orman, King, Bloomberg, or a centrist candidate from either party jump into the race as an independent.