Prime or zoom lens for video — which should I buy first?

Depends on what you shoot — but here's the decision in one line: controlled work → prime first; uncontrolled work → zoom first.

The case for the prime (a fast 35mm or 50mm equivalent): wider aperture for low light and real subject separation, sharper for the money, lighter, and — the underrated part — it teaches composition. When you can't zoom, you move, and moving changes perspective, not just framing. Every filmmaker who learned on primes frames better for it.

The case for the zoom (24-70 equivalent): weddings, events, docs — anywhere moments won't wait for a lens swap. One body, one lens, every focal length in the bag. The cost is speed (slower apertures) and the temptation to stand still and zoom, which flattens your coverage.

The trap to avoid: buying focal range instead of aperture. A slow 18-300 "do everything" zoom does everything badly in real light.

If the budget only buys one: most people shooting client work need the zoom's flexibility; most people building a directing eye are better served by the prime. Know which one you're becoming.