I found that Windows 8 ran almost perfectly. But, it dedicated allot of RAM making it hard to play some intensive Game's
I have 2.00GB Installed RAM with 1000gb Storage,
Let's see now, Win8 has a pretty nice UI and comes with some pretty nice features such as the large windows store that keeps on updating all the time (that's a pretty cool feature to have on your pc btw), but win8 also lags like hell (don't know if this only happens to me or not, but for me it super lags!) and sometimes for me it overheats and the fan makes so much noise just while i'm on Minecraft.
Win7 on the other hand has a nice UI too, it's fast, beautiful, doesn't come with the same large features as Win8 but is pretty good for some professional work and could get the job done, i have choosen win8 before but that was before i found out how laggy and shitty it could get (on win7 i can play Minecraft all day long and it won't even overheat and the fan wouldn't make any noise at all).
So yeah, i would go with Win7!
Note: i used to go with Win8 Pro now i'm going with Win7 Ultimate.