The 5C is the first iPhone that does not have an edge in quality feel compared to the (mostly) plastic competition. I personally am not always keen on buying the latest and greatest. My wife and myself decided to upgrade to an iPhone 5 just last week. Why not the 5S or the 5C?
Compared to the 5S we saved 200 Dollars. We are not big gamers so the extra horse power was not needed. The battery improvement would have been nice, but we haven't had any problems getting through a day on a charge and 10 % is not a huge increase that will suddenly make the need to charge regularly vanish. So I know there are other reasons to buy the 5S and I believe it is a good value. But if you do not need the improvements, why spend extra?
Then, why not the 5C? Four reasons: Weight, No 64GB option, no white front panel and plastic back. We take a lot of pictures and videos of our little kid and also have huge music libraries, we like to carry around. So 32 GB is not gonna cut it in the long run - as we do not want to rely on the iCloud only (lost most of my bookmarks that way once). The weight is a nice advantage because we are both long distance runners and it feels just a little better to carry less weight while running. The plastic back is certainly a matter of personal taste as is the white front panel. I always had a black version so far (original, 3GS, 4S) and went with the white one this time for a change. If I needed colors I could always get a case. And as the phone is something I intend to look at daily for two years why would I even want a color that annoys me after a couple of months. My wife always had a white iPhone and wanted to stick with that (impossible in plastic cause the front panel is black).
So that is a long and pretty personal description why I did not choose the 5S or 5C. In the end I think, the 5S will sell great while the 5C will present trouble, if my wifes opinion with the preference for the white front panel is more common among women (I know several who all currently use a white iPhone because they think of it as more elegant). We will have to see. Early sales seem to be not very encouraging. All models available for launch day on all carriers in the US - three days after the start of taking in pre-orders. That does not look like Apple calculated the demand properly.