I would suggest taking professor Li's class:
Class notes are quite clear and organized. He had all the materials prepared in draft paper that would be presented in his notes with oral explanations in the lectures.
Homework questions are carefully selected. You can review after class.
Professor was always willing to answer questions.
Many students complained that the exams were too hard and they were too different from quiz. It was true. However, you can find all the question types in previous homework. If you really want to have a solid foundation in calculus, the exams will motivates you to work hard and understand key points.

Although this class was challenging and took a lot of time and effort in my opinion, Professor Li did his best to help students understand the difficult concepts. As a new professor, I think he improved greatly throughout the quarter and got better at helping students. I would highly recommend going to his office hours. Although he does not usually give the final answers to homework problems, he will start them for you which is helpful. Even if you cannot attend office hours, he usually would be willing to stay after lectures and help students with homework problems or answer questions. Overall, going to him for help was the best for me since I did not have a good TA.
The homework for this class was assigned weekly every Monday and due on Sunday. Although there were not that many problems, many of them were challenging resulting in the homework taking a good amount of time. I definitely would recommend working on the sections of homework throughout the week and not waiting until Sunday to do the whole assignment. I usually would complete the problems for the most part during the week so I could ask questions during office hours on Friday. This helped me get 100 on all the homework assignments (although he does end up dropping your lowest homework score).
The quizzes were fairly easy. They typically consisted of 2-3 problems and were given in the last 15 minutes of discussion. He also dropped the lowest quiz score at the end of the quarter.
I found the exams in this class to be challenging. However, they did get easier and I think this had to do with the professor wanting to make the second midterm and final not as challenging as the first midterm. Li also offers 2 grading schemes in this class. Scheme 1 included: Homework: 15%, Quizzes: 10%, Midterm 1: 20%, Midterm 2: 20%, and Final: 35%. Scheme 2 included: Homework: 15%, Quizzes: 10%, Best midterm: 30%, and Final: 45%. At the end of the quarter, the professor goes in and calculates which scheme works in your favor. Having the second scheme as an option helped me out a lot since I did not do well on the first midterm.
Overall, although this class was challenging for someone who is not naturally good at calculus, I would say that Li was a good professor who wanted to help students.

Although Math 31B will always be a difficult class, I felt that Professor Li wanted his students to succeed, especially if they put in the effort. He is very helpful and will always try his best to answer a student's question. I would recommend attending his office hours, since I found that this helped answer any questions that I had on the homework/tests. For this class, there were 10 homework assignments, 3 quizzes, 2 midterms, and 1 final. I found the homework and quizzes a good way to boost your grade, while the midterms were the most difficult. But, he made a good portion of the final very similar to the practice final, which made the final a lot easier than both of the midterms. What helped my grade the most was having one of my midterms dropped so the final was weighted more heavily and I believe this was beneficial for many other students in the class. Overall, Professor Li was great and I definitely recommend him as a math professor.

ONE BIG PROBLEM: Lingfeng went to USC!!! Jokes aside, the class is decently easy and straightforward, and I felt like I pretty much mastered the concepts before the final. I was able to do this despite skipping most of this class. Difficulty ramps up significantly weeks 7-10 and into the final. Also, watch out for TRUE/FALSE questions on the tests, specifically the final, as they are worth way to much. I think I got pretty much every FRQ right on the final but 4 missed MC put my final exam grade down 20%. Other than that a fairly good course.

Easy class mid professor.

My experience with this class is that if you do the homework problems yourself and truly understand each one, you will be able to ace his exams. The midterms are not too bad, you just really need to be able to understand patterns and applying what you learn. The final was more like a huge unit test which did not focus on anything which was before midterm 2. There is a lot of partial credit given so even if you got the wrong answer on a problem, the amount of work you showed adds up and helps you gain some points. Overall, I think the class is extremely doable as long as you are willing to put in the effort.

Pretty solid professor. Always posts notes online and follows the textbook. He's also very considerate. One time, I forgot to submit my homework on Gradescope and he let me submit it late. He also has pretty reasonable tests and if you practice enough proofs, you should be sufficient enough to get a good grade in this class.

I will warn you that the final is very hard though. Definitely prepare for the final 2 weeks in advance unlike me.

Details on class:
Two grading schemes:
25 HW + 20 Mid1 + 20 Mid2 + 35 Final
25 HW + 30 Best Mid + 45 Final

Overall I liked 31B taught by Professor Li but I wouldn't say this is an easy class.
Good things about this class:
1. The professor is very helpful, he replies to your emails in a timely manner and is often willing to stay after class to answer your questions.
2. Workload is manageable, he gives less work during Thanksgiving break/midterm week.
3. Professor Li is genuinely a nice and chill person.
But there were things that went not so well:
1. Classes are not recorded or broadcasted.
2. Midterms were hard but the Professor was generous with partial credit.
3. The professor's teaching could've been clearer.

Li was a good professor; he seemed to be concerned with our success and was open to our feedback as a relatively new professor. Lectures and discussion didn't require attendance. There were 2 midterms, a final, and 3 quizzes (in discussion section). Discussion sections usually just involved practice problems. The quizzes were pretty easy (I had a good TA who helped us prepare for every quiz) and the exams were tough, but I think if you study a lot you can do well (I'd recommend doing just a lot of practice problems). For all of the exams, Li gave us a few formulas, but you weren't allowed to have a cheat sheet, so memorizing all of the formulas and theorems is tough. Lectures weren't posted anywhere, but you could get that week's notes from him every Friday after class.

This is actually for his Math 32A course but since its not on bruinwalk I'm doing it for 31B.

Linfeng Li is a great prof. He goes through material in a very concise yet understandable way while making it interesting. He also records lectures. There are 3 quizzes throughout the quarter and the lowest score gets dropped and the lowest hw score. He has 2 grading schemes- one where 2 midterms are counted and one where only 1 is; he automatically chooses the higher one for you. Midterms are very chill and similar to homework problems and final is easier than midterms. He actually cares about the students and wants you to do well. Would recommend.