I thought most of the candidates except Cruz and Paul, either held serve or excelled on various questions.
Trump, to his credit, did not waiver one bit from his brash, in yer face style that got him to where he is in the polls. He was savagely blunt on various questions Fox attempted to trip him up with, particularly running as an independent, donating money to the clintons, evolving on abortion, and building a border wall. His best moment (imo) was when he more or less threatened Megan Kelly at the beginning after she raised his record of misogyny on social media.
Bush, I thought also did well. He could've been more assertive with some of his answers, but I get the feeling his strategy coming in was to portray himself as calm, above the fray, and statesmanlike. He quite correctly didn't get into it with Trump and stayed in neutral territory, which left a few pundits scratching their heads because he didn't really move the needle in his favor. But I think in the long run that will benefit him.
Walker was also quite neutral and avoided attempting to score points off Trump. Good call once again. He wisely took his airtime to list his perceived positive accomplishments.
Rubio did better than most expected. He was comparatively articulate and squeezed a lot of good/substantive points into his answers. He did come across a bit as a deer in the headlights schoolboy on the first day of class at times, but he certainly didn't put a step wrong.
Kasich scored a lot of good points, and perhaps did significantly better than most expected. Like Rubio, he was one of the few who actually got into policy substance.
Christie, wasn't particularly effective. Got into a pointless handbags with Rand Paul over NSA bulk data collection. Otherwise didn't really do much to stand out.
Carson, seemed completely out of his depth anytime he was asked a specific question. Always seemed to pivot back to vaguely unrelated talking points. At one point he seemed to make a claim about the US Air Force in 1940, when the Air Force didn't exist until later. Didn't do much to raise his profile.
Cruz, completely flat performance imo. He was obviously there to not make any mistakes and go after Hillary, which he did, but at the same time, he squandered his chance of standing out against the others.
Huckabee, next to worse performance. The questions seemed to pigeon hole him into social conservative themes like transgender people in the military. He rightfully came across as a TV pundit masquerading as a vaguely poor Presidential candidate.
Rand Paul, absolutely calamitous from the start when he interrupted a Trump answer to go after him, then got into it with the likes of Christie and Trump later one as well. He made a weak pivot on the who created ISIS question and basically did little to cast himself as a legitimate contender. If anything, he came across as a bit of a desperate muppet.
Big winner - Trump, Bush, Walker, and Rubio
Big Loser - Huckabee and Paul
Honorable mention - Kasich, who is probably attempting to talk his way into a VP nomination, especially with the importance of Ohio.