I've been frustrated with most QR Code readers. Most in the iPhone App Store are crap. Either they don't read the codes very well, or they don't support all of the QR Code features - that is, assuming they decode the QR code, they'll all jump to an embedded URL, but that's not the only supported QR Code function: they can also have embedded "business card" information that's supposed to add to your Contacts list, can initiate an SMS message to a pre-defined address, display a message in a pop-up window, and several other things.

Various ones I've tried have problems with QR Codes that aren't 100% as they expect them to be. For example, one feature of the QR Code format is that some percentage of the code can be damaged and the code should still be decode-able. For example, if the threshold is 25%, then the code should be decode-able as long as ANY 75% of the code is visible. This is to support decoding codes that have damage due to normal wear and tear, such as scratches or pen marks on labels that can occur in any orientation. Some QR Code publishers will take advantage of this and replace part of the code with some silly graphic to make it unique. I don't like it when they do this, but if the code is otherwise valid per the specs, then a proper reader should be able to decode it. Another problem that one of them had was that it would decode QR Codes only if they were in black ink.

The AT&T QR Code reader is okay on the quality side, but it has the annoying feature of uploading all decoded URLs to the AT&T mother ship before redirecting to the actual page, presumably so they can collect data on QR Code usage.

Like the OP, I'm interested in a quality QR Code scanner for iPhone. If anyone knows of one that a) decodes all valid QR Codes, including those that are "damaged" below the acceptable threshold and those in colors other than black, b) supports all QR Code features and not just URL redirection, and c) doesn't upload data to a mother ship, I'd be very interested. Although such an app should be free and included in iOS (IMHO), I'd be willing to pay $10 for one that actually worked per the above.