I recently purchased the Chemistry case made by iFrogz with the rainbow watercolor design for my iPhone 5c. The fit is great and everything is completely covered or protected. The case snaps on and stays on becoming a second skin to the phone without adding unnecessary bulk. The external case is shiny and somewhat slippery polycarbonate plastic while the inside and edge is TPU for cushioning. There are no seams on the exterior meaning there is nothing to take away from the smooth feel in your hand. There are no sharp edges making it very comfortable to hold.
The watercolor rainbow design is whimsical and adds to the 5c's colorful design in a good way, though you can only tell the phones color by looking at the rear camera opening which allows the phone's color to be seen. The regular price is $20.00 and $16.99 is better but I found the same case on AT&T's site for $14.00 plus tax and in-store pickup.
I have a few cases for my 5c from INCIPIO and SPECK which are good cases but the INCIPIO Feather Clear does not cover all of the phone but does provide good protection. The SPECK Candyshell provides the same protection as the iFrogz but adds some bulk to the phone. The case from iFrogz gives great protection without adding bulk. This in turn allows it to maintain the slim feature of the 5c while protecting it.