iPhone 4 lags badly if use iOS 7 in it. iPhone 4S is the better last phone to fully utilise iOS 7.

On the other hand, I have updated to iOS 8. First impression is that the UI are even friendlier to some degree. Only noticeable thing is that its eating up battery slightly faster than iOS 7.

Whoever is running Yosemite and wanted to restore iOS 8, do make sure you install Xcode 6.1 Beta before doing so, else the phone will be temporary bricked due to iTunes 12 crashes during restore