A service contract is a set of PHP interfaces that are defined for a module. These service contracts are stored in the app/code/VendeorName/ModuleName/Api/ directory and Data interfaces resides in app/code/VendorName/ModuleName/Api/Data.
Magento 2 Open Source suits best for small ecommerce stores as this solution provides tools that can help merchants to build an online store in a fast way with no hassle and minimum expenses.
Magento 2 Commerce Edition recommended for B2B companies, enterprises, and companies with high volumes of website traffic, a variety of product catalogs, wide global reach, business complexity, or plans to expand in the future.
Magento 2 Commerce Cloud is a managed, automated hosting platform for the Magento Commerce software. Magento Commerce Cloud comes with a variety of additional features that sets it apart from the on-premise Magento Commerce and Magento Open Source platforms. Fastly Content Delivery Network (CDN), Image Optimization (IO), added security with generous bandwidth allowances, Dedicated hardware, High availability infrastructure, 24×7 email support and many more.