If all other things are equal, Linux. Unfortunately, things are not equal.

I prefer Linux over OSX (actually, I think that even Windows is better desktop environment than OSX). But I really love my Macbook Air, it's the best machine I've ever had. Under OSX it runs smooth, it rarely spins up the CPU so it's silent, never overheats. Under Linux, not so much. As a consequence, the battery under Linux drains considerably faster.

So in the end, I've adjusted to OSX, I don't like it but I've learned to live with the annoyances (which are subjective anyway). My time is mostly spent in the console/browser and iTerm2 is really great terminal so in the end, I've come to the conclusion that installing Linux on Macbook is not worthwhile (and I've thought about it a lot).

I use both at work (+ Windows) and prefer GNU/Linux the most. Second would be Windows and only then OSX

This is sad, but apt-get and most Linux package managers require sudo to install stuff. Homebrew doesn't. I love Linux, Mint with Cinnamon that was my main desktop environment for 4+ years, but I'm typing this on a mac.

OSX for dev, Linux to deploy on for test and prod

Linux