Monolith: One deployable unit. Simple to develop and deploy. Hard to scale individual components. Changes affect everything.
Microservices: Many small services. Independent deployment and scaling. Complex operations. Network overhead.
Start monolith, extract microservices when needed. Don't say "microservices" in interviews without justification. "I'd start with a monolith. When the payment team needs independent deploys, we'd extract payment service."