Barack Obama. I can't think of a better outcome for the incumbant Democrat than the effective three way tie of Romney, Santorum, and Paul.
First, the Republican participation was reportedly not much different than in 2008 - hardly a groundswell of "anti Obama" fervor. Second, Romney (the presumptive eventual nominee, by all accounts) did not budge from his "25%" poll numbers - continued evidence that the religious right is soft on the moderate Massachusetts governor with the curious religious beliefs. Ron Paul's strong showing bodes well for a potential third party run. And the christian right's coalescing around Santorum (abandoning Bachman and Perry) just means that Romney will not deliver a knockout vote anytime soon.
What's not to like? The longer Romney has to scrap for the nomination, the further right he'll be pushed, and the less palatable he'll be to moderates come November.
And as an added bonus, the Romney rooted PAC negative ads really pissed the hell out of Gingrich, who will, I suspect, remain a potent sniper chipping away at Romney's armor for the next few weeks. Next to Romney, Gingrich is, I think, the candidate who could give Romney a run for the money, so Romney taking him out removed a bit of a wild card that could have caused trouble.
I may be wrong, but the Republicans being equally split across moderate, libertarian, and christian right sectors seems about as good a portent as possible, looking towards the November elections. And if the economy continues to show signs of growth (despite the efforts of the do nothing, obstructionist House of Representatives), I think Obama isn't in too bad shape.