It's the question I get most from people about to build their first app: Firebase or Supabase? Both give you a database, authentication and storage without running servers. Choosing well saves you weeks. Here's the criteria, not the trendy answer.
What each one is, in a sentence
Firebase (by Google) is an ecosystem of ready-to-use services with a real-time NoSQL database (Firestore). Supabase is an open-source alternative built on PostgreSQL, a relational SQL database. Both solve the same thing; the difference is how you think about your data: in 'documents' or in 'tables'.
When to pick Firebase
Pick Firebase if you want maximum speed to start, effortless real-time (chats, notifications, live collaboration), and you don't mind thinking in documents instead of tables. It's what I use in most of my products because it lets me ship fast, and its auth is one of the simplest out there.
When to pick Supabase
Pick Supabase if your data is very relational (many connected tables), if you already think in SQL, or if you care about avoiding vendor lock-in with an open-source base you can take elsewhere. Its dashboard and SQL queries are a delight for structured data.
There's no 'good' one always. The task decides: real-time and speed to start → Firebase; relational data and control → Supabase.
My real advice: don't get paralyzed by this decision. For your first app, either one gets you to production just fine. Pick one, build it, and learn the rest along the way. The expensive mistake isn't choosing 'wrong'; it's spending weeks comparing instead of building.