DP review has tested the iPhone 5S’s camera and – surprise – it’s awesome. At ten long pages (all requiring a click to reach, as is DP Review’s annoying style) it’s an epic read that you’ll probably want to add to your Instapaper queue, but you can always skip to the conclusion and read the rather amusing list of “bad” points that the reviewers have come up with to make the article “balanced.”
Whatever it is you want to know about cellphone camera sensors, you’ll probably find it in DP Review’s absurdly in-depth article on the subject. It details not only the common misconceptions about megapixels, but also many real world differences. And it contains the diagram shown at the top of this post, showing the size differences between the sensors in various phones, measured in pixels.