CPU and RAM
When it comes to raw power there is only one winner here on paper - the new HTC One (M8). It sports Qualcomm's latest quad-core chip - the Snapdragon 801 - clocked at 2.3GHz and that's backed up by 2GB of RAM.
The iPhone 5S on the other hand sports a 1.3GHz dual-core processor and just 1GB of RAM - but don't let that put you off.
Because iOS 7 only needs to support a handful of devices Apple has managed to optimise the platform to ensure it gets maximum performance from its modest components.
What does this mean? Well it means you're not going to see a great deal of difference in terms of navigation, speed and load times between the iPhone 5S and HTC One (M8).
We did notice that the One (M8) tended to be a shade quicker than the 5S, especially when it came to more intensive tasks such as loading a graphically heavy game, but you're unlikely to be slowed down by either device.
With its larger screen and more powerful innards you may well be fearing for the battery inside the HTC One (M8), and to be fair at first we were too - but those fears were quickly extinguished.
HTC has squeezed a slightly larger battery into the One (M8) over its predecessor - up from 2300mAh to 2600mAh - but the real star of the show here is the Snapdragon 801 chip.
In our tests we found that even with heavy usage the HTC One (M8) was able to last around a day and a half on a single charge, and if you cut out gaming and movies it'll see out two days.
Move over to the iPhone 5S and things don't look quite so stellar, although it's not bad news.
The current standard we expect from out smartphones is a full day of usage and the 5S delivers that - but that's all the 1560mAh battery gives you.
For those of you who like to carry spare, fully charged batteries in your bag there's some bad news, as neither device offers a removable power pack thanks to the unibody designs of the handsets.
When it comes to looking at the cameras on the HTC One (M8) and iPhone 5S it gets a bit interesting as on paper neither handset sounds like a top of the range mobile snapper.
The iPhone 5S boasts an 8MP camera, while over on the HTC One (M8) you get two sensors on the rear of the device with the main one equivalent to just 4MP. Compare these to the 16MP Galaxy S5, 20.7MP Xperia Z2 and 41MP Lumia 1020 and it appears to be a losing battle.
We found what the iPhone 5S produced the better general images when heading out and about snapping various scenes, but it's in post production where the One (M8) really fights back.
The new One (M8) comes out on top in terms of tricks, with an impressive array of post-capture tools allowing you to easily and quickly create a really unique image.
The best feature here is U-focus, which allows you to select the focus point of an image after the photo has been taken. This means you can choose whether to highlight an object in the foreground, or a landscape in the background.
It's all thanks to the Duo Camera setup on the rear of the new HTC One, where the second, smaller lens only captures depth information, rather than a complete image.
Both devices sport front facing cameras, with the iPhone 5S equipped with a 1.2MP offering for those all important Facetime calls, while the new HTC One boasts a 5MP camera - perfect for a cheeky selfie.
The HTC One (M8) is a high end smartphone and thus commands the same lofty price tag as its predecessor. While AU$899 is a lot of money, the new HTC One is no more expensive than its Apple counterpart.
In fact the 16GB iPhone 5S, which doesn't feature a microSD card slot, will set you back AU$869 while the 32GB is AU$999 and the 64GB variant clocks in at a whopping AU$1,129 SIM free.
It means the new One (M8) is priced reasonably well and it falls in line with the likes of the Galaxy S5 and Xperia Z2, while also having the advantage of going on sale before both of them.
So which should you get - the iPhone 5S or the new HTC One (M8)? Well, that's actually up to you rather than us, as both are top quality devices offering rather different experiences.
If you're heavily embedded in the Apple ecosystem, have plunged hundreds into iTunes or simply want a more palm and pocket friendly mobile the iPhone 5S is the one for you.
Its glamorous design is just as premium as that of the HTC One (M8)'s, but its more compact chassis makes it easier to transport - although movie watching and gaming aren't quite as good on the smaller, lower resolution 4-inch display.
Anyone looking for a real powerhouse of a mobile they can flaunt in front of their iPhone wielding friends will want to get their hands on the HTC One (M8).
We love its all-metal unibody design, making it look and feel fantastic and that helps justify its lofty price tag a lot better than the all plastic Samsung Galaxy S5.
If we were to choose, we'd nab the new HTC One (M8) over the iPhone 5S - although with a larger iPhone 6 looming on the horizon we could be drawn back to iOS in a few months time.
Watch our full HTC One (M8) video review here:
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John joined TechRadar over a decade ago as Staff Writer for Phones, and over the years has built up a vast knowledge of the tech industry. He's interviewed CEOs from some of the world's biggest tech firms, visited their HQs and has appeared on live TV and radio, including Sky News, BBC News, BBC World News, Al Jazeera, LBC and BBC Radio 4. Originally specializing in phones, tablets and wearables, John is now TechRadar's resident automotive expert, reviewing the latest and greatest EVs and PHEVs on the market. John also looks after the day-to-day running of the site.