Gerald Ford almost certainly, and it would be a virtual walk to the nomination, depending on when he finally decides on running. Those conservatives who would be opposed to him don't have the kind of candidate to rally around to win, unless you count Phil Crane who might gather some small support. The Moderates would be fine with him, as would most Liberals.
If not Ford, then probably George Bush, in the sense that he had developed a campaign that was far more effective than that developed by his opponents, and Reagan's death shouldn't effect that eventual outcome. It may be more of a fight, with Baker and Connally the other two main contenders, but I see Bush taking the prize.