When would be a good time to buy an iPhone? And iPhone 4S or 5?

I'm 19 and I'll be working a summer job this year. I plan to use some of the money to buy myself an iPhone but I don't know when a good time would be or which model to get. I know the 5S is coming out later this year and the price of both phones will probably go down but I'm slightly impatient and would like to buy it by the end of August. Also, I realize they're both practically the same phone, just that the 5 is bigger and probably has a better camera and the 4S will be yesterday's news sooner but I'd be saving myself $100 by getting it instead.

I'd wait for a bit, apple have just gotten into some legal trouble because of the way they've been doing their taxes so if you really want an iPhone then their prices may or may not drop in a couple of weeks depending on what happens to them.