The verdict
For a small team selling products to consumers, I would lean towards Shopify, because the app store and the point of sale tools save you building things. For a team that sells to businesses, needs price lists, or has a developer who wants clean APIs to build around, pick BigCommerce.
Price out your real set-up before you decide. On Shopify the plan is only part of the bill, because apps, themes and payment fees add up. On BigCommerce, the payment provider you choose changes what you pay, and the plan follows your sales. Either way you are building on their platform, so rebuilding elsewhere later takes real work. Compare both on the integrations you need, not on feature lists.