For custom printed stickers what is the best print file format?

Generally vector artwork is best. That's genuine vector artwork not an image embedded into a vector file format. If that's not available then a high res PNG or JPG is usually good enough. Because the majority of NFC tag print is quite small then the resolution of artwork can often be quite low and still print OK

However for the best print high resolution 200dpi or better or vector EPS PDF AI SVG is best
Seritag - 11 Jan 2023