Server-side development suitability: 1) Both module systems are viable for server-side development, 2) CommonJS has historically been the standard for Node.js, 3) ES Modules are now fully supported in Node.js with .mjs files or 'type': 'module', 4) CommonJS offers better compatibility with existing Node.js packages, 5) ES Modules provide better future-proofing and standardization, 6) The choice often depends on specific project needs and ecosystem compatibility, 7) Both systems can be used together in modern Node.js applications.