Should i buy an iPhone 4 now or a blackberry? any other phone?

-So i have a Sony Ericsson Satio now, but i want to buy an iPhone 4...should i buy it? please explain why i should or shouldn't.. thanks xx

i am used to touch screen so don't really require a qwerty keyboard.iphone 4 is better
iPhone 5 is coming out soon.
depends on what you need it for