Definitely go with Windows 7. I recently rebuilt my desktop and went with Windows 7, a worthy successor to the venerable Windows XP. My brother-in-law bought a new laptop with Windows 8 and I had a tough time even installing a free anti-virus program. With Windows 8 pretty much everything you were familiar with has changed. The touch screen features are not at all intuitive like on the Apple I-pad.
That because win8 has its own built in antivirus/antimalware built in. Its what microsoft does. they increase funtionality in the operating system. You can add a 3rd party firewall to later versions of windows, too. But why ? (And it will be a bitch to setup)