I've just got a Z2, at long bloody last, and already I can see that I'll be using this more than my M8.
Why?
Well, the M8 is nicely protected in the dot view cover (but this is quite cumbersome and the novelty of the retro display soon wears off) but outside of the case, the phone feels vulnerable.
Wait, what? The Z2 with glass and the M8 with metal? Yes, I'm serious. I feel like the M8 will dent or scratch far too easily (I have the gun metal grey model) whereas the Z2 has both front and rear protectors applied and feels better in the hand. Obviously my opinion but if you have both side by side, you may agree with me.
Then there's the camera. Having quickly realised that it's quite hard to ever use the unfocus feature to get a good result (as in you have to make sure that there's nothing on a similar 'plane' that doesn't remain in focus when you use it), I disregarded that as a gimmick. What I do like is the immensely quick AF, but there's no camera button and the image quality for anything but close up portraits ends up disappointing simply due to the lack of pixels.
Frankly, I'd have sooner had two image sensors - one Ultra Pixel for awesome close ups at night, and a 'normal' 13-20MP camera for outdoor photos, perhaps producing 5-8MP images and giving the ability to have a lossless zoom. Rather like the Lumia 1020 and indeed the Z2, albeit only for a very short distance.
I know you can use a gesture/flip to open up the camera on the M8, but it's not as good as a dedicated button.
Oh, and the M8 isn't water proof. That's quite a thing once you've been used to it on the Z, Z1 and Z1 Compact. Like an incredibly wet weekend in Cornwall, taking photos of flowers and trees at a huge garden. Nobody else was taking photos with their cameras, but I was. Some of the colours of a garden in bloom, during the rain, are quite incredible.
But it's not just using the camera, but using the phone in the wet and not worrying about it in the slightest. It's also nice to be able to 'wash' the phone to clean it up occasionally.
I can see why Samsung realised it needed to add water resistance to the GS5 and I think HTC might have to consider its options too. Once thought of as a crazy gimmick popular only in Japan appears to be spreading.
Battery life: So far the M8 is excellent. Can't fault it for that, but I am seeing good signs on the Z2 too. From getting it set up last night, I was down to 19% and figured it would die any second, but that 19% equated to 11 hours according to the phone. In reality, it was down to 10% by the time I went to bed at 2am - and my battery widget claims it loses 1% of battery for every 19 minutes. The M8? 18 mins.
That's going to be a close call I reckon.
Speakers: No doubt about it, the M8 wins here, but the Z2 has for the first time got close. There's not as much kick on the Z2 front-facing speakers, although I'm yet to fully experiment with the audio settings. I'd say that the M8 will still win this, but the Z2 is surely the nearest competitor. The Z2 also has the noise cancelling technology and support for other accessories, like stereo microphones, which might be of interest to people recording a lot of video. [I've not tried 4K video yet, as it seems to cause all sorts of heat related problems, which can even lead to warping of the casing - a major issue that I feel compelled to mention here until such time Sony fixes the issue].
Finally, performance: Another close match given the same SoC, although the Z2 has 1GB extra RAM (which to be honest I doubt is necessary, but gives Sony something to shout about). I'm yet to do any benchmark tests on the Z2, but obviously other people have already done this so the figures are pretty similar. HTC offers a developer menu option to run at max clock speed all the time, while the Sony doesn't - but does let you restrict the CPU to further save battery in the Stamina menu.
Anyway, I guess it's not for me to write a full comparison review on here (it's early days for me with the Z2) but these are my thoughts as to why I'd side with the Z2.
And this is a comparison between the M8 and Z2, so I am not mentioning the Galaxy S5 now.
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