I like 7

But I heard many people said it's very slow when I use for iPhone 4 so I'm very confused between upgrade it or not.I'm using iOS 6 Anyone help me ?

Go for it. I have used it with iPhone 4 and never had any problems, it made my phone faster and everything worked smoothly. Just make sure that everything goes well with the update, and update through your computer, not on the phone itself. You won't regret it.

iOS6.