we found the Nexus 5 to consistently offer better pictures in nearly all scenes. One of our biggest complaints about the HTC One is the over-processed look it gives pictures, and while we know that comes out of necessity with only having a 4MP camera it just comes off looking wrong to our eyes. In both auto and HDR mode, the One took consistently brighter pictures than the Nexus 5, but did so at the expense of adding lots of processing and grain to pictures — often over-exposing them far more than we'd like.
Although it took darker pictures when compared side-by-side to the One, we found the pictures coming out of the Nexus 5 to be more true to life, leaving shadows where they should be and highlighting other parts just the right amount. The difference is even more dramatic in HDR+ mode, which seems to gather a drastically better range of color than the HTC One's HDR mode.
The Nexus 5 vs. the HTC One | Android Central