I run all 3 os's and i think they all have their strengths. OSX is good for its simple UI, It is intuitive and simple. Windows is a good all rounder and my main os. (not so keen on w8 but it did grow on me through my MCSA).
I run several windows and some Linux servers. Linux seems to be good for low resource needs but you need to be able to bang out commands like there is no tomorrow. Win servers are again just like working on a standard pc (unless you have core installed and you have to work in powershell) i do see the benefit in all 3. But is someone held a bullet to my head and told me to recommend an os to them it would likely be Windows 7! Its been out long enough to be very stable and well supported. And i think there are a good few years of support left in it!