I mentioned before that it's a win win situation iOS 8 beta is running great on the 5s so updating is a mute point in my eyes the i6 would have to blow me away to for me to upgrade but then again my carrier upgrade is due in November so only time will tell
I'll be doing both, actually. I'll upgrade my 4S to iOS 8 to see how it runs and then I'll buy a new iPhone soon after. How soon depends on how big the screen is. Without an increase I'll give the newest Android phones a quick look before I make my decision.
For me it all depends what it offers over what I have. And being that I have a 5s, the iPhone 6 would really have to blow me away to upgrade. IOS8 will run great on the 5s and will get all features except maybe one or two they hold for the iPhone 6 due to hardware requirements, most likely the hi siri without needing to be plugged in which I can live with. I will upgrade my 5S to IOS8 for sure.