I just got the Otterbox Defender for myself, and the HTC case/cover that converts into a stand for my wife. The HTC case is surprisingly good for what it is. Mostly she just needed light protection mostly for the corners, since she already dropped it and now has the shiny aluminum showing through the black paint on one corner. Converting to the stand works well, and so far she is happy with it. She was most worried about adding too much bulk, but this worked well, even with the flap.
I got the Defender, mainly because I need a lot more protection, and I have been using a Defender on my Evo3D for years. I have been hugely impressed by their quality, and especially their support. I have to say that so far, I don't think they hit a home run with the Defender for the One. The outer rubber, I have mixed feelings about. It is much harder than the older cases. This may make it less prone to stretching, which I know some people had problems with. It is also much smoother. I don't think it feels as comfortable in my hand, nor as grippy. On the plus side, it is nowhere near the lint magnet that my Evo3D Defender was.
I'm not sure I like the overall design either. I know that having the IR blaster in the power button introduces extra problems when designing a case, but their choice didn't makes sense to me. Because the cutout isn't front and back, it actually makes it a little annoying to hit the power button. Not a huge problem, just a minor annoyance to me. If you have smaller fingers, it may not bother you at all.
The only major complaint I have really, is the builtin screen protector. The Evo3D Defender seemed to be nice and tight against the screen. This one has a noticeable gap, enough so I hear almost a tapping noise with every touch to the screen. It also seems to make it harder for the phone to register my touches. I have installed the latest update, and it registers fine without the case. It may just be a bad case. I have a second one that should get here Monday. I will see if that one is any better. I'm also not really thrilled that the screen protector doesn't cover the capacitive buttons. Not a huge deal, but something you might want to know ahead of time.
All that being said, it would be easy to think I don't like the Defender for the One. I'm actually still very happy it. Unlike some other Defender cases, it really adds little bulk to the phone. Not to say it is slim by any stretch of the imagination., but it gives good protection while not being huge. Also, one of my biggest complaints about the Defender for the Evo3D, was that the raised edges made it very difficult to register touches at the edges. The Defender for the One appears to have fixed this issue. I am thrilled by that change.
Overall, I am still happy to be using another Otterbox Defender. I am probably a bit biased because of how well their support worked for me in the past. I have seen other cases similar to this that look like they might actually resolve some of my complaints with the Defender, but as long as their support stays top notch, I'm happy to stick with them. Of course that doesn't mean I won't be trying some other cases. :-)