IPhone 4, 4s, 5. What's the difference?

I'm looking into getting an iphone, and I want to know if there is a major difference between the three latest models. If there isin't I might as well save me some money and get the 4, or even the 4s. And since apple is always putting out new stuff, how much could it really change right? Well thanks I hope to get some good feedback

Different letters but the 5 is 1mm larger

The 4s is an improved 4, and I think the best bang for the buck. The 5 is stretched and weighs less (stretched so you get an extra row of apps) and also faster. I've heard the main thing about the 5 is it's more designed around Siri (voice control). I have a 4s and was thinking of upgrading to a 5 (with a trade in it's almost a fair swap I heard), but the 4s fits nicely in your pocket, and the 5 just seems bigger than need be.

This is the actual Apple comparison page, it should help.
http://en.wikipedia.org/wiki/IPhone_5

The iPhone 4 just has a completely different shape from its predecessor, the 3GS.

The iPhone 4s has a better camera, and is faster, and has Siri, a virtual assistant that uses voice commands.

The iPhone 5 has a larger screen, and is taller, thinner, and even faster. The problem with the iPhone 5 is that it uses a completely different plug, so you have to use special docks or an adapter to connect regular iPhone connectors with the newer plug, called "Lightning".

So, to help you with choosing your phone, I would pick the iPhone 4s, as it's both fast and it uses regular iPod/iPhone connectors, along with letting you use the same case as the iPhone 4, since they are both the same size.