Budgets and time are limited, so the question isn’t really "website or Instagram" in the abstract — it’s "what should I invest in first, given where my business is today." Here’s a practical way to decide.
If your customers are actively searching for what you offer
Businesses like clinics, service providers, restaurants and local shops usually benefit from a website first, because customers are actively typing search queries related to what they need. A website is the tool that captures that specific, high-intent traffic.
If your product is highly visual and discovery-driven
Businesses selling visually-driven products — fashion, art, food presentation, design work — often see strong results from social media first, because the platform is built around discovery through visuals rather than search intent.
The honest middle ground
In practice, most businesses need both eventually: social media to build awareness and engagement, and a website to convert that awareness into a lead, a booking or a sale, and to be findable through search independent of any platform. If you have to start with one, invest in whichever channel matches how your specific customers currently look for businesses like yours — and plan to add the other soon after.