In terms of basic word processing, internet usage, web browsing, file manipulation, listening to music, etc. there's really no significant difference between Windows, OS X, Linux, and other Unix-like systems (like BSD). The only major considerations would be:
You require/prefer a specific software for work that is only compatible with a certain OS family
You are coding software in a language that is not OS independent
You particularly like some specific feature/functionality from some OS
Basically, you'll know if there is an OS that is better for work based on what job you have. If you can't think of anything that you know for a fact does not exist on another OS, or have been told by a coworker you must use a specific OS, then just use whatever you're most comfortable with.
As for gaming, generally Windows is still king there, but OS X has made considerable progress on that front. Hardware selection is poorer on Apple's machines (ex: I don't think Apple sells any machines with GTX 970s or 980s in them so if you want to use one with OSX you'll need a Hackintosh) but just looking at the current line of iMacs they seem like decent (if overpriced) lower to medium tier gaming machines. If gaming is your primary concern I'd say Windows is still for you, but if you currently have OS X it still has options.
Similarly, Linux has made a good amount of progress in terms of game availability, but still suffers from a much smaller library than PC, can be much harder to setup than Windows or OS X, Linux ports can often be poorly optimized and so performance suffers (ex: Dying Light in Windows runs at 60 FPS no problem, all settings maxed out, 1080p resolution. Switch over to Linux however, on low settings it struggles to keep 1080p 60FPS), and once you get away from Debian derived OSes, installing Steam gets a little trickier.