It depends how “friendly” is your Instagram handle. If it’s short and easy to write or it has some special characters - for instance “beanandween” it’s easy to type, “bean&ween” requires an extra step, not much but still, you want to make it easier for your future customers.

The QR code has the advantage that people that have difficulty typing in smartphones, or dyslexia or any other disability that prevents them to type/read correctly, can easily scan it

You could use a qr code pointing to your social media and a qr to your website where they can add their email.

Instead of a QR code, you can have a NFC tag in your stall where people can easily tag and go to your website/social media.