Choose the file from the job
SVG is the file to send a printer. It has no pixel grid, so a business card and a banner can use the same file. PNG is a fine fallback. Use 1024 pixels for a flyer and 2048 pixels for a poster. Scaling a small PNG up makes the modules soft.
A sheet of several addresses exports at up to 640 pixels per code, which is enough for a contact sheet and too coarse for a large individual print. Download a single code when that one code will be printed large.
Size, contrast, and a proof
For an arm's-length scan, keep the code at least about 2.5 centimetres wide, including the quiet zone. Go larger for a window, a poster, or a code people will scan from across a room.
Print dark modules on a light, solid ground. Glossy laminate and strong glare can hide a code that looked fine on screen. Scan the first printed proof with two different phones, in ordinary room light, before you print the rest.