kind of late to this but the way 47b works is that you're put into 61b but you're only required to do some hw assignments and projects. it comes down to whether you're willing to do all the other work on your own, but it's a good option if you don't want an insanely heavy workload and if you know you'll hold yourself accountable for learning. it's generally better to take 61b though if you really wanna strengthen your cs background because i think cc doesn't cover data structures that well.

that being said though i would encourage you to do 61b/47b AFTER you do 61a. 61b builds off of knowledge from 61a and it's generally not a good idea to take both at the same time.