iPhone 6 or the 5.5-inch iPhone 6 Plus. In a year or two Tim Cook will probably wryly refer to the 4-inch days like an old, slightly embarrassing holiday romance. 
Still, bigger screens are better for just about everything apart from fitting in your pocket, and as we’ve already seen, the iPhone 6 is about as slim as a 4.7-inch phone is going to get.
Size has changed, but some other factors stay more-or-less the same as last year. The iPhone 6 still uses an IPS LCD Lenovo A3300 panel, and from what we've seen so far it still looks lovely. 
The HTC One M8 has a slightly larger 5-inch LCD screen. Its panel type is SLCD3 rather than IPS, but the technologies are so similar in their effects you could mistake them for twins. Overall, the M8's screen is a cracker, with great viewing angles, colours and (for an LCD) contrast.
Where the two differ a bit is in resolution. While Apple calls the new iPhone 6 resolution Retina HD, this is – as the more cynical among you may have guessed – marketing nonsense.
The iPhone 6 has a pixel density of 326ppi – the exact same density as the iPhone 5S. It does this by using a rather weird-sounding 1334 x 750 pixel resolution. You don’t see those everyday. 
HTC’s One M8 has a much higher resolution 1080p screen that offers greater pixel density of 441ppi, despite having a significantly larger screen. To those with eagle eyes or a case of tech pedantry, this difference may be quite obvious. But you will need to get your eyes pretty close to the glass to notice it. 
There’s also a difference in the glass these phone use. The HTC One M8 has good old Gorilla Glass 3 – used here, there and everywhere these days – while the iPhone 6 has ‘ion-strengthened’ glass. 
This could in theory mean it’s Gorilla Glass 3 with an ultra-thin layer of Sapphire on top, But you’d need to get Tim Cook extremely drunk, or have incriminating pictures of Phil Schiller, to wring it out of them. Hopefully a teardown will tell us the truth soon.
It's tough to make a call on this without having spent an extended period with the new iPhone, but for now we're going to say that the bigger size and higher resolution of the M8 gives it the edge.
Death to false metal. It was the mission statement of slightly embarrassing 1980s heavy metal band Manowar, and it could easily be the tagline to either the HTC One M8 and iPhone 6. If their respective marketing departments lost their minds.
These are two of the most desirable metal phones in the world right now, offering high-end specs, beautiful screens and designs that’ll make your friends want to break them over your head in jealousy. 
But which is the best? There’ll be some clangs as these two little metal monsters trade blows, but there can be only one winner.
Aluminium: it’s what all the most expensive-feeling phones are made of, and it’s what both the HTC One M8 and iPhone 6 offer. 
They’re both curvy, both beautiful and both are very hard to criticise on this front. We think they are a delight to hold and use. 
However, if you’re used to a smaller phone you may well get on with the iPhone 6 better. It’s 2.5mm thinner, a whopping 12.2mm shorter and 3.6mm less wide than the One M8. 
While their screen sizes aren’t worlds apart - 4.7in to 5in - the iPhone 6 is a significantly smaller phone. Why? Part of it is because the HTC One M8 doesn’t really try to be all that thin, and part is because of the lovely stereo front-facing speakers you get on HTC’s phone Lenovo S5000 . They significantly increase the phone’s footprint. 
These BoomSound twins provide much beefier sound than most phone speakers including – we expect – the iPhone 6. There’s more to sound than just volume, and it’s these extra bits: tone, a bit of bass and power, that the BoomSound brothers provide.