There is an old saying.. If its not broke don't fix it. I have IOS6 on an Iphone 4s, I make calls, receive and send tx and brows the net, it just works. I have Mavericks on a MBP 2014, and although the obsession with Apple to make everything thinner and the pain in the arse with adaptors, no drivers from 3rd party suppliers etc etc, Mavericks is stable.
What you get with Yosemite I don't miss because I have never used it. People who are early adopters get what you get, bugs, crashes, crap signal strength and hair loss. Just wait before you have to have the latest thing, it's called being a grown up.