Spree Commerce empowers the world’s sellers by providing them with a versatile, modular open-source ecommerce platform that allows for easy integrations with every major third-party service. Spree benefits from a vibrant, international community of over 500 designers, developers and other professionals who have enthusiastically contributed to the growing platform since 2008, making it one of the top open source projects in the world. In 2013, the company launched Wombat, a sophisticated piece of integration software that connects any store to any service or application. Wombat automates the backend operations of storefronts running any ecommerce platform including Magento, Shopify, Bigcommerce and Prestashop.
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.
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.