Opti Contact is a program that provides you with an easy and quick way to generate QR barcodes containing your contacts' details. The application brings you a straightforward interface, communicates well with Mac's Contacts app, and immediately offers you the results you need.
When you launch this utility for the first time, the program asks for permission to import the contacts from your default address book tool (Contacts app) and you need to click the Allow button. Afterwards, you can select which contact item you wish to be generated as a QR barcode and choose a destination folder for the output image.
I like the fact that the application allows you to preview the barcodes before exporting them.
Nevertheless, two issues bother me about this program: it supports only one output format (PNG) and it doesn't let you select what contact info to show up in the image (name, mobile phone, homepage, etc.).
Still, the application comes without a price tag and creates the necessary barcodes within seconds. So, I'd say it's up to you to decide whether it's worth installing this program on your computer or not.