Humans have killed each other over the silliest of reasons (when seen from the outside), but not yet over the choice of favourite operating system. Like computer languages, frameworks or databases, we can have our favourites – and the best for a project may be our least favourite.
I have developed on the three main flavours – OS X, Windows and Linux/Unix. I like something about all of them, but I know if I had the best of the 3 combined, the result would not be as suitable as the three as separate systems.
In the end my effectiveness on each is about the same, so I am happy to use whatever the project requires.
Of course the same does not hold through for IDEs. They are all crap exect … (enter your favourite here).