Upgrade to iPhone 5c/s or no?

I'm currently using an iPhone 4 and am considering upgrading to one of the newer models. I'm only doing this because my phone has been running slow even prior to upgrading the software to iOS 7 and now it almost unusable at times due to constant crashing. However, I figured since I'm getting a new phone anyway, I'd give an Android, Nexus, or some other brand user the opportunity to convince me to make the switch.
Please give me some insight as to what I can expect by switching. I really only care about overall speed, and app availability. Please be specific!

Get the iphone 5s it's amazing