HTC is really pushing their One branding, which is smart, because for years they've lacked a very coherent branding strategy. They've never really followed in Apple or Samsung's footsteps when it came to branding their phones, and set some expectations for their current and upcoming devices that bear that specific brand name.
Even Sony had the Xperia brand, and LG had the Optimus brand, although in LG's case I think they should also change it soon to a new one in the same time as they are launching some devices that really feel "premium" and puts LG on the map when it comes to making quality high-end devices. LG actually has very good specs in some of their high-end phones, but until more recently at least, their software had bugs, and most of their devices still have either poor design or poor build quality, or both, which makes people ignore them as high-end devices.
Getting back to HTC, the One strategy is working for them very well so far, but they are not just going to let it go. Now they are setting up a photo challenge, where they dare you to guess which photo was taken with a HTC One phone, and which was taken with a "professional digital camera" (whatever that means, but I doubt it's a DSLR, and if it is, it's probably a very low-end one). This is still a marketing stunt, but it's a good way for them to show that their pictures are in the digital camera range now.
I still think the Xperia S has the best camera on the market right now, but the HTC One X one might be second best, maybe not necessarily due to image quality, which might be about the same with Galaxy S2 and iPhone 4S, but because its high performance in low-light conditions thanks to its f/2.0 lens, which should be better than both of those.