My advice is to wait. The ones currently being sold are the pre-release ones they designed based on rumored specs, so they're not a good fit. Evidence is they print "2014 iPhone 4.7 Inch" on the package since they didn't know it'd be called iPhone 6 when they produced the case.
I got 3 just to make sure (1 from Amazon, 1 from Speck.com, 1 from Best Buy) and none of them fit right because of the back bowing out.
If iPhone 5 is any guide, it should be 2-3 weeks longer and we'll start seeing the cases made post-launch, so they'll actually fit based on the actual product, not rumored specs.