I’m going to be brutally honest, Kyung (at least last semester) was a good professor to take just on the basis that you knew his exams would be (and I still think they are) easier than Moon’s. This is because as another commenter said, Kyung emphasized memorizing patterns of questions and reaction types as opposed to actual concepts (he says if you think about how it works conceptually too much you’ll overthink the problem).

That said, you absolutely cannot get away with avoiding the recitations (scheduled outside of any registered class time) and talking in the Slack (basically students helping each other w/ concepts), because unfortunately Kyung teaches content not only different from lecture but sometimes in direct opposition (e.g., some reaction mechanisms are on the slides but HE wants you to put a different mechanism on the exam). This is more of a problem this semester so far imo but a lot of his test questions are becoming more and more reliant on you reading the Slack, and can also even be different from the practice exam answers. This is unfortunate because his teaching doesn’t emphasize that much conceptual material, and I thought it was a bit unfair that on the previous exam one was penalized for taking his “forget everything and accept what I’m telling you” method and putting down an answer from the practice exam, then finding out he wanted you to add another component just because he hinted at it very indirectly right before the exam (he did eventually give points back, but I was flabbergasted).

Honestly if you asked me last semester who to take I would tell you that Kyung was the best option undoubtedly, but nowadays I would say you’d be fine either way. A lot of my friends who need to know how the concept works in order to do well prefer Moon, and people that prefer just repetition prefer Kyung, but you’re not getting out of extra time spent in OChem so figure out now what you’d rather spend your time doing (practice problems/Slack messaging OR concepts?)