What's the difference between the iphone 4 and iphone 4s?

What is the difference? Which should i get?

Siri.

Right now iphone 4 is free with contract but 4s is 100 $$$$$$$. The 4s has siri which is useful if you are lazy to google something. If you have money to spend 4s is not a bad choice, but if you are just looking for a smartphone that can do basic stuff than i would take 4

For better camera get 4S, for best phone use Android device.

IPhone 4 has no siri,
iPhone 4S runs faster
iPhone 4S is higher mg I guess.