Currently I'm planning to stay on 7.1.2 until my 5s no longer works.
As a general rule I try to keep my tech on the OS version it came with so that an update made for newer/faster hardware doesn't ruin the performance of mine (exp: iOS 7 on the iPhone 4 or iOS 8 on the 4s).
You might be able to get away with updating to the next iOS one time but updating year after year is just asking for your device to become a laggy mess and needing replacement.
It's really sad that Apple feels it's ok to stop signing old iOS versions even if the customer has already paid for the hardware they now own and already have the files/capability to downgrade if it weren't for Apple intentionally blocking it (aka planned obsolescence).
iOS 8 doesn't have any features that really wow me. Maybe an app will come along down the road that somehow changes my mind.