BigCommerce is much flexible in terms of switching themes  and it is more industry specific when it comes to features. 

Shopify has got better designs and also offers wide range of choices in features as well as templates.

Is BigCommerce safe?

Yes, BigCommerce provides highly secure and safe shopping experience to the customers by following best practices. 

BigCommerce provides a secure shopping experience for customers by keeping their security systems up to date with the best practices. The Payment Card Industry Data Security Standard (PCI DSS) is an information security standard that organizations must adhere when handling credit card and debit card information.