What are major dffrences between the iphone 4 and 4s?

I have the iPhone 4, would it be pointless to upgrade to the 4s? If the 4s is just like the 4 then it would pry be better to just get the 5s. I need to know differences between the two phones if their is any.

4S is free on 2 year contract so no reason to get 4, rule that one out.