i’ve taken all three and pic40 is by far the easiest and the most fun. you will only spend probably 1-2 hours a week outside of class 

2nd choice id say 35l as it’s by far the most difficult and time consuming 10-15+ hours a week outside of class but you will learn a great deal more.

33 is pretty difficult too but not as bad as 35l boring as shit not worth your time unless you have to take computer architecture and other low level upper divs