What source of traffic is higher quality - Facebook or Pinterest?

It all depends on your marketing communications strategy and the actual tactics that you execute. Some businesses find either social platform to perform better than the other one, sometimes both, sometimes neither. For example, based on my own experience, food blogs do great on Pinterest when the visuals are professionally produced (See my friend Allyson's website https://www.pinterest.com/allysonreed/, she makes everything on her own, including coking the recipes, taking the pictures, etc.) That, in combination with a great promotion plan (influencer outreach, large loyal follower base, among others.) Some businesses do great with Facebook when they use the right balance of paid media and organic content posting. Facebook offers great targeting options for paid media. Unfortunately, you do have to pay for paid media on Facebook, they have forced businesses to do so as a way to reach to followers, organic reach is harder on these days since the algorithm hides a lot of your content in the newsfeed.

Get your analytics set up and define what your best channels are, reinforce the low performers as well as the top ones. Use aligned strategies across channels but prepare unique executions on each, do not just copy/paste from one channel to the following one.

In your business category, see what others are doing, for example:
https://www.facebook.com/Craftytude

Contact me for my counseling service. It is the cheapest service here. I will give you strategies and secrets that will prepare you very much. I hope you keep them for yourself only because it is the fruit of the effort of years of experience.

Facebook would be my first answer but it truly depends on what your traffic is for.