Linux or Apple.
It's not that easy in my neck of the woods. I have commercial boxes on RHEL 6.X and RHEL7.X. My local development machines are on Federa 22. The company laptop is a Windows 7 Enterprise. My big fire breather has Window 8.1 Pro (OEM). It will be going to Windows 10 on the 29th. The big machine also has VMware 6.0X Player to run all the other operating systems that I have to support, but lack space for physical hardware.
I still have 3 Fedora 20 system that I haven't had time to upgrade. Apple? Well, yes. iTunes running in the big machine hosts the backups for the iPad Air and nano devices. If you do this for a living, you have to keep the whole set of machines running smoothly.