Windows 7 or Windows 8 is more matter of personal choice.
I prefer neither of them.. Don't get me wrong, they might be the one to go for most of the people, but I use Linux, just because from the moment I used it, I am in love with Linux. It is fast, safe and a lot powerful especially for someone like me who knows programming and can write scripts.
And also gaming is now getting better on Linux, ask a Linux gamer like me...
Even if you don't know any scripting stuff and all, it still is a very powerful OS which is also almost secure and at last is free.
Windows might be the choice to go for people who use it, but a word of advice from my side. At least try Linux once in your life and try to explore it. It is free after all.
If you want to try linux, then try Linux Mint. It is the best beginner friendly OS. People coming from Windows might like Zorin OS, it looks and behaves more like Windows.
Anyways what OS you want to choose it upto you.
Out of Windows 7 and Windows 8 I would choose the latter and put the start menu app on it and forget about the Metro.