iPhone 5c or 5s?

My buttons on my iPhone 4 are not working well so I was talking to people at work to try and find a trusted place to get it fixed and they told me it would cost less to upgrade to an iPhone 5 through the Apple store in the mall… the question is… iPhone 5c or 5s. I’m told about $99 for one and $199 for the other. $99 is obviously more appealing financially but I wonder if the 5c case is durable enough and how the plasticky case would hold up. I just don’t know.