I run Vista Ultimate-64, Win 7-64 and Win 8-64 on three seperate HDD's.
Actually I am sticking to Vista for now since it boots up and shuts down quicker than the other two.
For an old game I have started playing again CoH, on Vista it runs fine.
On Win 7 it refuses to keep the screen in full screen so that I have to keep hitting the 'max' button to get full screen, but it soon reverts back to 'max' again.
On Win 8 it always crashes on a certain level.
I quite liked Win 8-64 that I bought when on offer from MS (for £24.99) in December 2012, and after installing 'Classic Shell' I can run it as per the layout of Win 7. I hate the 'start' screen with the tiles, and the Metro layout.
There are a few more niggles with it, but, I think it is a bit better than Win 7.
But, because of the niggles on those two, I just run Vista which doesn't cause any problems.........and maybe, also to annoy the Vista haters..