The last OS X I used before El Capitan was Lion 10.7, and sadly I have to say it's considerably worse.
Some of the bugs I face everyday are when using and external monitor, it scales back the windows to the retina aspect even in the external screen after it wakes up from sleep, so I have to rearrange them manually evertime I wake the computer up.
Furthermore, sometimes when I download a file using Safari, the "downloading" icon in my dock reimans at 0% until i reboot the computer.
Low transparency mode is heavilly bugged with the use of an external screen, sometimes the animations are laggy and when I shut down the computer with apps open, when I reopen it, they don't work and when I right click the dock to quit them, it always shows "Application not responding".
Seriously Apple need to step up their game, I remember the days of Snow Leopard when absolutely none of these issues were present, so updating to a (possibly) even more buggy OS X is absolutely out of the question.