Which is better? Amazon or shopify

Shopify is a better option for professional sellers who need a standalone site on their own domain. It's considerably more customizable, and lets you create a much more 'on-brand' presence than Amazon. It's much a better solution for dropshipping.
For small businesses and startups, Shopify may be a better option due to its lower cost, ease of use, and customizable design options. For medium to large businesses with more complex needs, Amazon's larger customer base, marketing and advertising options, and international reach may be more beneficial.