Preliminary Nielsen numbers show that “The Tonight Show with Jay Leno,” with Sarah Palin as a guest, beat “Late Show with David Letterman,” with Mitt Romney on the marquee. The breakdown was 5.8 million viewers for Leno and 3.7 million for Letterman, with ABC’s “Nightline” as 3.3 million.

Although Romney had the smaller audience, it’s hard to see how he didn’t have more to gain from the late-night primary than Palin did. Relentlessly characterized as out of touch during the 2008 campaign — Mike Huckabee labeled him the kind of guy who’d lay you off, to paraphrase — Romney instead proved why politicos seek the late-night arena: He was likable. His book tour is a way for him to appear as the Republican with solutions, a cool head amidst all of the hysteria. Like Obama, he can’t do angry populist rhetoric. Heck, Romney appeared even unfazed when recounting the story of the guy punching him in the face on his flight back from the Vancouver Olympics. “He broke my hair,” Romney quipped.

Romney may be the anti-angry populist, but he didn’t criticize the tea party, but explained its origins and offered words of understanding. And rather than offer a blanket takedown of healthcare, or even say that President Obama needs to start from scratch, he argued that the approach should be state-by-state rather than the federal government. (Perhaps it is the same difference). By posing as the dumb guy who knows nothing, Letterman challenged Romney, particularly when it comes to spending, and the former Massachusetts governor conceded some points but offered others, namely that it’s the trillion dollar deficits that have people most concerned. Letterman didn’t challenge Romney’s assertion that the “problem isn’t the insurance companies,” but rest assured plenty of Democrats already are.

Had Romney gone on Leno, I’m not sure he would have come across as well. His humor may have come across as forced and the one-liners contrived, because of Leno’s style of interviewing, which is more about eliciting gags than getting to the substance. It’s not wrong — these are still entertainment shows — but more often than not Letterman let Romney get his points across, and challenged him, in his own satirical way, when something didn’t make sense.

Perhaps Romney’s best line was one that distinguished him from Palin, his prospective rival. He praised her. But when Letterman alluded to his spat with Palin last year, Romney quipped, “She has a rifle, you know.” It was a joke, but a reminder of how different these 2012 prospects will be if they both get in the race.