I have worked with many companies on marketing experiments to decide their effective channels.
First, establishing your specific target will help you know which channel is best since you can see your demographic information on Facebook and can translate a lot of that into Pinterest.
Second, have you sent any traffic via ads through those channels to your store? Through Google Analytics you can assign values for traffic origins. The quantity of traffic vs the expense vs the end result will equal the quality you are receiving.
Would you like to discuss specific actions you can take to measure these transactions via a phone call?
There are many opinions on which social media platform drives most traffic to your website. Specifically as your platform is selling products, crafts specifically, Pinterest is an amazing tool! Conversion rates from Pinterest boards to purchasing is far more than those on any other social media platform. A great tip: Pin from your website to your pinterest boards, this drives traffic back to your website/craft store once the pins are clicked on. You can view analytics on your store and pinterest to evaluate your follower demographics and cater to those.
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: