HTC has been working hard to win market share from Korean competitor Samsung for the past few years.
HTC had some success in 2014 after a poor critical response to Samsung's Galaxy S5 led many buyers to consider jumping ship to HTC's excellent One M8.
However, one year later Samsung has moved to see that history doesn't repeat itself and has released the completely reworked Galaxy S6 that redefines the firm's handset offering.
By comparison, HTC has played it safe and released what in many people's minds is a reworked, rather than rethought, smartphone, the One M9.
To see how the Galaxy S6 and One M9 compare to the Apple iPhone 6 you can also check out our triple head to head review.
Design and build
Visually the Galaxy S6 looks completely different to past Samsung handsets and borrows design elements from Apple and Sony smartphones. Specifically, Samsung has built the Galaxy S6 with metal sides and Gorilla glass front and back faces.
The One M9, on the other hand, looks almost identical to its predecessor with 'Boom Sound' speakers and a rounded metal back that wraps round to the Gorilla Glass front.
In fact, the only immediately noticeable design change is that the One M9's sides are a different colour to its back.
We found the Galaxy S6 slightly more comfortable to hold than the One M9, mainly because of the Galaxy S6's 143x71x6.8mm dimensions and 138g weight, which make it 3mm thinner and 19g lighter than the 145x70x9.6mm, 157g One M9.
However, it's also because its sides are slightly rounder than the One M9's which has edges that feel a little sharp.
The Galaxy S6 also comes with more custom design features than the One M9. Key positives are a custom heart-rate monitor on the back and a fingerprint scanner in the front-facing physical home button.
The heart-rate monitor is designed to take advantage of fitness apps, while the fingerprint scanner lets users set the Galaxy S6 to unlock only after they have proved their identity. We found the fingerprint scanner a particularly useful feature that allowed us to secure the Galaxy S6 without needing to remember a complex password.
The Samsung Galaxy S6 feels noticeably sturdier than its predecessors when it comes to build quality, but the One M9 has the edge.
The metal frame makes the One M9 noticeably more scratch and mark resistant than the Galaxy S6, and the latter's glass back is an outright dirt and blemish magnet.
This is surprising as Samsung claims that the materials used in the Galaxy S6 are 50 percent tougher than on competing metal handsets.
Winner: The Galaxy S6
Samsung made a big song and dance about the Galaxy S6's 5.1in, 2560x1440, 577ppi, Super Amoled display when it unveiled the phone at MWC, claiming that the screen displays 70 percent more pixels than its predecessor.
By comparison, HTC rested on its laurels with the One M9, loading it with an equivalently specced 5in, 1920x1080, 441 ppi, Super LCD3 screen to that on the One M8.
Comparing the screens head to head, we found that the Galaxy S6 claims rang true. Text and icons were super sharp and the Galaxy has wider viewing angles and a higher maximum brightness than the One M9.
Colours were also richer and deeper on the Galaxy S6, which remains one of the best calibrated screens we've ever seen.
That said, despite not being a major upgrade, it's important to note that the One M9's display is still very good.
It's always difficult to spot differences in sharpness between smartphone displays that break the 400ppi barrier, and we noticed a difference in sharpness only after a prolonged period staring at the displays while cycling through a variety of high-definition pictures and screen tests.
Colours on the One M9 are fairly well balanced and have a 'cooler' feel than most competing manufacturers' handsets, which can have the settings cranked up to the point where they oversaturate colours in a bid to give them more 'pop'.
Winner: The Galaxy S6
Next: Operating system and performance