That's the wrong question to ask if you're serious about FPGA design. If you were, you'd ask about devices, maybe devboards (though that's not a very good question either because you have to pick a devboard for the project, not the other way around), and then you do whatever it takes to get stuff done. OS is just a tool, as long as it can run the tools you need, that's all you ever need, and doesn't matter what that OS is. If you place your feelings/preferences/religion above "getting stuff done", you're not really serious about whatever it is you say you want to do. For example, I have both Windows and Linux because some tools work better in one OS or another - AMD/Xilinx tools work better in Linux, while Altium Designer only works in Windows. And don't tell me that one OS is more convenient than another - that's completely beside the point, as in professional setting OS is only used as a launcher for a professional software you need to do stuff, and all mainstream OSes are equally capable of doing that.