I've been using the HTC One since its release in April, and like many, was excited about the looming Max version. Early reviews seemed pretty negative, but user reviews sounded pretty positive so I decided to give it a whirl. I'm on day 6 of my 14 day trial and I'm really liking it.
At first, I did think the size was awkward, but I'm adjusting quickly. I'm one of those people who was disappointed by the lack of memory expansion in the original One, so I'm fully taking advantage of the micro sd slot with the Max - music, photos, videos, etc. I was down to ~3 gigs on my One, and I was having to constantly upload to cloud storage to keep even that space available. No longer the case. Loving all the freed up internal storage.
I'll need some more time to determine if the lack of OIS with the camera is significant. I have noticed a few times where it took me multiple attempts to capture a good, non-blurred shot. Hopefully that won't continue.
The fit of the back cover on this phone is pretty rough. Unless my particular model is faulty, HTC did a poor job with the construction of the back cover closing mechanism. There shouldn't be too many times I HAVE to remove the back cover, but when I do, the process of trying to fit it back in place is beyond frustrating.
My only other gripe is the noticeable lack of simultaneous Voice and Data unless you're on Wi-Fi. I never noticed how much I used mobile network while on speakerphone, etc. until I got roadblocked trying to do the same with the Max.
All in all I'm really enjoying the Max and am strongly leaning towards keeping it over the One. I'm surprised by the lack of more positive reviews for this phone. I'm only concerned that due to its limited availability (sprint and verizon only), HTC won't make it as high a priority as the One with updates. Time will tell on that.