While the iPhone 5S is obviously quite a more capable and powerful phone than the iPhone 5C, some of these improvements have actually caused for slightly less reliable performance. To be specific, the 5S’s 64-bit processor is causing apps to crash twice as much as they do on the 5C or original iPhone 5.
Apps running on the iPhone 5S have been measured to have a 2% crash rate, while apps running on the 5C only crash 1% of the time. In other words, only 1 in 100 apps you open will crash for you on the 5C, while 1 in 50 apps will crash for you on the 5S.
It’s not that the 64-bit A7 processor is worse, it’s just that many app developers haven’t gone and properly added 64-bit support. Currently, most apps are only designed to run on the 32-bit architecture that every other iPhone uses. If developers don’t go in and properly configure their app to work with the 64-bit hardware, there can be some memory issues that will cause the app to crash more.
Apple is trying to get all its developers on board when it comes to updating their apps with 64-bit support. The company has a guide posted online on how to transition 32-bit apps over to 64-bit here.
If you could only afford a 5C instead of a 5S, you can take this as a small, yet temporary, victory.