iPhone 5S will be announced first of the two - here's why and how I see it going:
-Apple Store updates
-Stats on apps, devs blah blah blah
-iOS 7 re-announcement (including a few new feature highlights)
-iPhone 5S announced (iOS 7 will be demoed on an iPhone 5S)
-iPhone 5C as the "One more thing" - similar to how they did the iPad 4, then the iPad mini.
They won't announce the phones BEFORE the OS and after announcing iOS 7, they'll want to do demos.....and of course, they'll demo on the 5S.
I think Macs and iPads are an October keynote.