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While I agree with others that more is better, if you can take only one course, I strongly recommend taking Andrew Ng's. While it is true that you don't need to be able to design and understand 'nets from scratch to be able to use them, I agree with most of the brightest minds in DL that you won't get too far if you don't at least have an intuition for the math behind it. And Ng's course really only gives you that - an intuition. It does an excellent job at ensuring participants understand the bare minimum to do any kind of serious work. Learning ${your favorite framework}'s API will be a breeze if you understand the "why" already.

I would take both. deeplearning.ai focuses more on math fundamentals, fast.ai takes a more coding oriented approach. It also has 2 classes: a beginner and advanced one. I personally prefer the fast.ai approach.

Add Udacity's DLF ND to the mix and do all 3 of them, they are all a bit different. Udacity's one has the inventor of GANs doing lectures there, so it's pretty top notch as well.