Which iphone has a better battery life?

[quemans]

I want to get a new phone, and I have a blackberry, the battery life is TERRIBLE.
I want to change to an iphone, but I heard lots of things, like the iphone 4 has better battery life than the 4s.
Are there any other phones with amazing battery life? and is the iphone a good switch ?

[eastline]

Is depend what version u use