I'm a scientist; I need to build stuff and run it in a sane environment. The best OS X for my needs was about 3-5 years ago; since then it's been going down. Starting with El Capitain they broke GCC so badly it's on longer usable. Unfortunately, no one else offers a Fortran compiler, a necessary part of scientific computing (yesterday, today and forever). I converted my Mac desktop to Linux and have been happier ever since.
OS X is still a decent laptop/terminal OS with an edge over Ubuntu. The retina display is beautiful and user things for the most part still "just work." But even there, they keep fiddling with no discernible movement forward. The "natural scrolling," for example. And all those iFeatures they fiddle with on every release? What a waste of time. I don't use iTunes, Pages, Mail or any of that other crap for my work.