What does 5C on your gold ring mean?

A gold ring will have the gold content inscribed inside. It may  also have the manufacturer's mark inside. 5C would be the  manufacturer's mark.

Which is better the iPhone 5 or 5c?

The IPhone 5c is not better than the IPhone 5 . Just because it is  new it does not mean that it is better . The IPhone 5c was made to  be cheaper version of the 5 .