Now is the worst time to buy a new iPhone
Don't do it.
Apple will announce the next model of the iPhone the week of September 7, likely on September 9, according to John Paczkowski of BuzzFeed, who has an excellent track record of breaking Apple news.
That means the iPhone 6 will be out of date and likely cost $100 less very soon.
I usually tell people not to worry about upgrading to the latest iPhone until we get this close to a new launch. Even if you buy the latest iPhone a few months before the new model comes out, you'll still be really happy with it. Apple does a great job at keeping older iPhone models up to date with the latest software and features. It can easily last you two years or more.
It's a different story when we get this close to a new iPhone launch. Unless your current phone is totally wrecked, hold out for the next model.