Facebook Ads vs. Google Ads: Optimizing for ROI

With Google processing over 70,000 searches every second and Facebook being a hub for 2.7 billion monthly active users, Google Ads and Facebook are obvious choices for PPC campaigns.
But is one better than the other? Are the optimization processes for both similar? What about A/B testing?
These are the questions optimizers need answers to before they can really reap the benefits of two very powerful advertising platforms.