Sony also is waterproof up to a certain limit, but I heard the Sony camera is also rather slow response (just like my current lousy Sony digital camera), not like Samsung one which is very fast with better picture as well.HTC One has one major disadvantage compared to the competitors - it doesn't have memory expansion options. No external cards and the HTC-ed OS is a little less user friendly compared to Samsung or Sony.
Having said that Samsung OS is really memory intensive and you have to constantly clear the memory otherwise the phone starts to go crazy with the little amount of memory left with all the bloatware that comes with the phone. And for some strange reason S4 heats up damn fast even with minimal usage.
Having used HTC, Sony, Samsung, LG and all with their latest OS upgrades, I find Sony is the best hasslefree phone. Works great, no memory problems and all that. Only issue is the stupid camera pinkish tinge on some of the cameras. Not all are affected by this issue though.
But ultimately the phone choice boils down to the TS and how intensive he is with the app usage. If he's like me then any phone will work great. If he's a heavy duty user he better choose the one with the best aftermarket Root support. Oh and Iphone5 has the best battery lifespan.
I myself is also considering to buy one, just also still undecided between Sony, Samsung, and maybe LG? Z1 seems rather too big and squarish IMHO. Size wise I actually prefer the S4 or the older Z but the older Z cannot take photos underwater despite it being waterproof as well.