Windows 7 or another system program

As you're an average user, Windows is the best choice as it's compatible with most of the software developed nowadays, it's easier to use etc. When comparing performance or specific uses (servers, mathematical calculations etc.), Windows usually isn't the best, losing to several distributions of Linux (as there isn't only one single "Linux", keep that in mind!), but its best pro is, as the famous technology says, that it is "plug and play" - you can get your computer working easily and fast.

Go for Win 7. It is very user friendly and 99% of games and software works on it. You will have many hardware and software (especially driver) related issues with Linux.

Just use Windows 7, it's the best out there. It might be costly, but it is well worth it. If you are not able to use it, try Windows XP, although that is outdated.

I think that there is no assurance for your system to be virus free as long as you connect to the internet and attached other media devices to your computer. I have used windows 7 and I liked it. I just had some troubles installing other 3rd party software. I switched back to windows XP because this is just so convenient for me. I had used linux once but I had problems on using it. Maybe I just was not familiar about their system. I think that if you only wanted to surf the internet and do basic operations with your system. Windows 7 will be fine for you but if you are into other stuff like editing videos and the like, I think that XP is the way to go.

The only good thing I know about linux is that it's virus free and it's free itself. But you will encounter lots of compatibility problems with the applications because it's difficult to find software that is compatible with linux. I heard that you will be working more on with terminals if you use linux and I find it complicated so I never tried using one. Go for Windows because it's user-friendly as well as most users have it so it's easier to find programs and fix it.