Actually, Samsung GS4 and HTC One has the same number of pixels i.e. 1920 x 1080 pixels. Because HTC One has a smaller screen by 0.3 inches, it has a slightly higher pixels per inch; however, it is humanly impossible to spot the difference between the two screens in terms of pixel counts.
Samsung GS4 comes with a Super Amoled display as opposed to One's LCD display. Viewing angles are better and colours are more natural on LCD screens, but there definitely are consumers out there who prefer the deeper black and blue and the saturated colours of super amoled displays (myself included).
The biggest downside of GS4 is its new TouchWiz. They added some "features" (or, more appropriately, "gimmick") that can hinder its true power of quadcore snapdragon 600 processor (clocking in at 1.9 GHz) or the "octacore" Exynos 5 chips that use two quadcore processors (A15 and A7, clocking in at 1.6 and 1.2 GHz in corresponding order). With the US variant (i.e. snapdragon processor), GS4 beats HTC One in almost every benchmark test; however, if you turn on some of its "features" like air view or air swipe, it will cause some lags, even for some of the more basic functions.
Camera is a bit of a complicated story. GS4 camera comes with a wide variety of features and it lives up to the samsung's reputation of incorporating one of the best mobile cameras in its flagship devices (i.e. Galaxy series). However, HTC One is noted for its excellent low light performance. I think it all comes down to what type of pictures (e.g. colour saturation, contrast ratio, details) a consumer would prefer that will ultimately determine which one of the two has a better camera. http://www.technobuffalo.com/2013/04/24/samsung-galaxy-s4-vs-htc-one-comparing-megapixels-with-ultrapixels/
-> Follow this link to see some pictures taken by these two phones.
Samsung GS4 is being widely distributed via multiple carriers in US, while HTC One seems to be limited to the major ones i.e. Verizon, AT&T.
If I had to pick between these two phones, I would most likely buy Samsung GS4; I've never had bad experiences with its products, so I would feel safest buying the GS4. I also adooorrrreee Super Amoled screen - high colour saturation just seems to make everything stand out more, for me at least anyway. As for the disappointing Touchwiz, I am sure that Samsung will release an update that will address some of the glitches it has.