Well, I've tried them all, including Bing.
There are only two that ALWAYS work as supposed to: Bing, and Esponce QR Reader.
But I find Esponce way better than Bing, especially when you scan a few consecutive QR's...also the options in that app are very good, and fantastic graphics in the app itself. So I switched from Bing to Esponce and never regretted it. I don't use Bing at all now on my Lumia.