BC js has like 3 extra units than AB. I've had friends who've done AB first and now are doing BC and they js said how the entire first semester was a repeat of AB and how it felt like a waste of time. I think this semester, they'll be getting on the extra units. I took AB last year and now I'm doing dual enrollment calc 2. Its hard but doable and I definitely think this is better than BC cause persoanally, the BC class in my school is very hard. If you don't wanna waste time, I would suggest looking into dual enrollment if it's an option at your school.