As a developer you should be able to work on any type of OS, if you can't do this then you still have to learn what it means to be a developer. However, we are not here ot criticise as much as finding which one of the 3 OSs are the best.
Most people say that Windows is the best, linux is hard to learn and Mac is to expensive, but none of them are thinking of what problem they try to solve. Let's have a look at some pro and crons for each one of the OSs.
Micrososft Windows OS
Everything works on Windows
Google is full of support for windows
Many hacker attacks
Free and open source
Require kernel knowledge
Almost imune to viruses
Mac Unix OS
Easy to use for non technical people
More complex then Windows OS
I think two comparable points is enough to decide what type of operating system you need. However, I do recommend a deeper research about what OS to chose but also keep in mind what problem you are trying to solve.