ID failed to activate no matter which finger I used to unlock it. I found a workaround by pressing the home button to activate Siri and then pressing the button again. After that it recognised the fingerprint without fail. This appears to be a software issue. Some users have complained that Touch ID stops working after a month or so of use, as noted in this BGR report. For them a software reset fixed the issue.
HTC One Max
HTC One Max has a fingerprint scanner on the back panel, under the camera. The placement is far from ideal as the scanner is difficult to access and users cannot see it while trying to unlock the phone. This is bound to cause a lot of frustration.
What's cool: You can assign fingerprints to apps. For example, you can use the left index fingerprint to open camera or Chrome. This lets you open the app you most use without going through the app drawer.
What needs improvement: A lot of things need to be done for the One Max's fingerprint scanner to be easy to use. The phone asks you to swipe downwards to unlock and more often than not, I found it hard to place a finger on the scanner. You have to swipe the finger a particular way for it to recognise your fingerprint. If your finger moves off that trajectory, then you will have to swipe again. This is frustrating, given that you cannot see the scanner while unlocking.
The problem with assigning fingers to apps is that if you forget which finger is assigned to which app, then it will be annoying to close that app to get to the home screen. It would be better to have a reminder on screen while unlocking to avoid this issue.
The device prompts you to set an alphanumeric password in case the fingerprint isn't recognised. It takes too much time to key this in, as opposed to a numerical passcode on iPhones.
HTC's implementation of the fingerprint scanner feels like a prototype that will get better in future releases, whereas Apple's is a quality addition to the iPhone 5S.