I personally will go for S4 but i am tempting to buy note 2
HTC one all the way.
Samsung doesn't have bigger camera. Megapixel doesn't mean anything, it's the camera sensor which matters. What HTC did is to increase pixel size(2 micron) , so that each pixel can catch more light, thus excellent performance in low light only comparable to Nokia 920.
What Samsung did is to decrease pixel size 1.1 micron from 1.5 micron,thus increasing the pixel count. As each pixel has much less area to catch light so they will be more noisy and consume more space as well.
This Megapixel war is just marketing gimmick, most dslr have 5,6 Megapixel. Most comp screen have 1028 pixel(full hd) display at best and even at 4 megapixel you will be downsizing your picture. I mean you won't be watching your pictures in billboard or something.
Only if you shoot in bright daylight and zoom your pictures to 100 percent then you can see more detail in s4 pictures. But HTC one absolutely kicks arse in low light performance.
Just check HTC one camera samples they are all over in net.
HTC one may take good pictures in low light but it don't take better picture in daylight. This comparison say it all
Samsung Galaxy S4 over HTC One
Bigger screen; works with gloves and air gestures
Higher resolution camera - 13MP vs. 4MP
Newer Android version - 4.2.2 vs. 4.1.2
Multi-window multitasking
Higher clock speed chipset
Expandable storage
User-replaceable battery of higher capacity
Additional sensors (barometer, thermometer, hygroscope)
Exclusive software features
Smaller, thinner, lighter
HTC One over Samsung Galaxy S4
Brilliant-looking aluminum unibody
Optical Image Stabilization, image sensor with 2µm pixel size
HTC Zoe, BlinkFeed
Front mounted stereo speakers, Beats Audio
FM Radio
For details comparison
Samsung Galaxy S4 vs. HTC One: Army of two - GSMArena.com