If you plan on buying the Nexus 6, here's a tip: always use the camera's flash if you want to take any photos in low-light scenarios.
In my most recent camera shoot out, I tested the iPhone 6 Plus, Galaxy Note 4, and Nexus 6 in outdoor, indoor, and low-light conditions. In most of the rounds, the Nexus 6 took acceptable photos, although Samsung and Apple's results were usually sharper, more detailed, and well-lit.
The biggest discrepancy between the three phones was evident in the low-light round. Take a look at the photos below. (Note: all photos were taken on auto at the same place and at the same time.)
Now here's a closer look at each of those photos. This one was taken with the iPhone 6 Plus:
And here's the Galaxy Note 4's version of that photo:
And here's the Nexus 6's image. You can barely see the subject of the photo.
Of course, you'll be using a flash to take photos in low-light environments like this most of the time. But this sample just shows how the cameras on the iPhone 6 Plus and Galaxy Note 4 are capable of taking in more light, which usually results in higher image quality.