Eventually settled on 8.1
I built a new PC six months ago. Long time Windows 7 user
I initially flirted with OSX, but could not get the thing perfectly stable and half the free apps I use were not available and couldn't use my paid for apps. Also the auto indexing would kill the Sata channels when indexing the SSD, causing the system to freeze until it finished (also and issue with windows 8/8.1)
Then I flirted with Linux (Mint), too many config options in too many different places and I just find the Gui an unpleasant experience, then there was the endless command line commands required to get certain apps working. And I couldn't use my Windows paid for apps.
I could have gone back to windows 7, but had a copy of Windows 8 lying around, installed and upgraded to 8.1
I use the system mainly in desktop mode (icons on the screen and in the task bar), with two monitors. And to be honest my workflow has not changed a bit compared to windows 7. If I do require apps that are not on the desktop, I don't really care if I find it on a full screen Start Menu or the little one as in Windows 7.
However I did do a quick install of windows 7 to see if there were any performance differences.
Windows 8.1 does perform between 5% to 10% better compared to 7.