Yes to get into a LITTLE more detail that lifeisabeach offered: the iPhone 5c does have some additional slight changes from the iPhone 5:
"The iPhone 5 is very slim and its thickness is 7.6 mm. The iPhone 5C is a little thicker having a waist of 8.97 mm. The 5C is wider and measures 59.2 mm to that of 58.6 mm of iPhone 5. The iPhone 5C is taller by a margin of 8 mm than the iPhone 5. The iPhone 5C weighs 132 grams, where the iPhone 5 weighs 112 grams. The 5C sports a beautiful plastic cover and the iPhone 5 has a metalling steel design. The camera on the iPhone 5C sports a BIS (backside illumination sensor) so that the photos are a lot better under low light. Both the phones support 3G/HSPDA and the CDMA2000 networks along with the 4G/LTE. But the iPhone 5C has been designed to be compatible with more LTE bands."
The iPhone 5s, on the other hand, has better everything. Better graphics, better processor, more RAM, more storage options, a better camera, the M7 motion coprocessor (useful if you're a fitness buff) and Touch ID as liab mentioned. If you can afford the extra $100, the 5s is a no-brainer. If not, you the iPhone 5c is still a fantastic iPhone and I love the way Apple "metallized" the back plastic so it doesn't feel in any way cheap or slippery. You'll see what I mean when you hold one, it's nothing like most "plastic" smartphones.