QR Code vs Data Matrix
Both are 2D matrix barcodes, but Data Matrix codes are typically used for very small industrial and pharmaceutical labeling where extreme density matters, while QR codes dominate consumer-facing uses because of universal smartphone camera support and instant visual recognizability.
Data Matrix codes can pack a similar amount of data into an even smaller physical footprint than a QR code, which is why they show up etched onto tiny electronic components or printed on medication blister packs. What they don't have is the QR code's three-corner finder pattern, which makes QR codes easier for an untrained eye to spot and trust as "scan me."
For anything aimed at a general consumer — a menu, a poster, a business card — a QR code is almost always the right choice specifically because people already recognize it on sight.