These things are always subjective, but probably the HTC One M8 for me (only just, mind).
* Build quality the best around, even better I feel than the Apple devices
* Screen one of the best around without resorting to battery draining gimmicks like QHD
* Sound quality from speakers and headphones the best around - good choice for an audiophile who doesn't want to compromise too much but also doesn't want to lug 2 devices around.
* Well judged and optimised OS with useful features over Vanilla - I still prefer Vanilla to use but this undeniably adds some useful features.
* Solid battery life - with the latest updates this is easily a 2 day phone with moderate use.
* Camera - some would say poor, but really it's only the resolution that's poor. It comes with some pretty useful functionality, its bloody fast (I'm sick and tired of slow, laggy cameras - I'm looking at you Google Play Edition and Nexus devices) and overall, the pictures look as good as anything else unless you zoom in.
* Processor - one of the earliest adopters of the still superb SD 805.
A close second for me would be the Z3 / Compact. The waterproofing ability is nice to have, and battery life is great, but I've read the camera isn't what its cracked up to be (some say they're poor on auto and some suffer with a pinkish spot in the picture in certain scenarios) and have heard mixed reports on reliability.
Followed by the G3. Lovely, good value phone, but what is the point of QHD which gives it worse battery life than the G2 without any tangible benefit in quality, and I found the default OS somewhat laggy and bloated like a Samsung.