Yeah I went through this whole struggle making qr code generators. It’s honestly kind of a nightmare and we should just invent something better:

• phones have different cameras and processing
• you want redundancy in the qr (the data is duplicated) but too much makes the dots too small and quickly toasts reliability
• short urls are everything, because then you can store less data and replicate it a bit more
• even still, various combos of data & phone will refuse a scan and cause support tickets
• people are still quite confused about how you’re supposed to scan them, so you have to explain on the card/flyer. Thankfully basically all phone cameras do it by default, but variations in the software don’t help, and the ux can differ a bit
• people don’t love sketchy links in general, and if the scan is taking too long to aim right, they will give up
• qrs are ugly and changes in color or adding logos quickly causes problems. Qrs don’t support logos, people just put em on and use the error correction (as if it’s a defect). Lack of spec means logos must be very small

So yeah how about a thing that works and looks good, next time our civilization reinvents bar codes

TL;DR: Pick L or M error correction depending on expected conditions. It is recommended to increase the error correction level unless it results in the QR code resolution (aka version) increasing. Many generators have this option. If you own the destination domain, use a short URL that is descriptive and contains/redirects to the page/resource in question, such as http://zooberlin.de/map?qr → https://www.zooberlin.de/wp-content/uploads/2020/06/karte_mobile.pdf?utm_campaign=poster (fictional example).

Can’t remember the last time I scanned a qr code, are they used in some businesses or something?