In the end, WooCommerce gives you more SEO-specific options overall, purely because of the fact that it's built on top of WordPress. The only problem is that your site speed largely depends on the hosting you go with. Because of this, the SEO category goes to Shopify. You don't have to worry about optimization much, and your speeds are always going to be top-notch.
Shopify, Big Commerce, Magento, IBM Commerce and Demandware have all been approved for Pinterest Buyable Pins. Would rather have Woocommerce be one of the first to get approved than one of the last. I have a major Pinterest Board and most of my traffic comes from Pinterest. Having Buyable Pins is not an option but a necessity at this point for my existing store.
BigCommerce is most easily compared to Shopify. Both platforms offer a similar experience when building an ecommerce platform. Like Shopify, BigCommerce offers a range of prices and packages tailored to different types of businesses. The platform is highly customizable if you are comfortable with some light coding. It is also possible to use themes and templates to build your website, but some of these will come at an additional cost.