I've been using iOS 9 as a daily driver, but only because my backup got overwritten.
There are bugs everywhere, personal hotspot over wifi hardly works, the occasional hangups etc.
Hanging on for beta 2 😉
As for El Cap, I like the graphics performance so far and I seem to run out of RAM much less often doing the same things on my 13" rMBP, however there are issues plaguing Safari such as pages not loading requiring a restart, the "Page was reloaded because of a problem" dialog which almost made me laugh since I see it on my 6+ ever so often, Messages have issues - not loading properly every time, I could go on and on 😉