Witn Win8 there's no choice to be made - AV is built into the OS (as it should be).
Nonsense.
Microsoft got into a lot of hot water with the competition regulators over the Internet Exploder bundling debacle. Just as IE is now an option, the bundled AV is also optional.
If the built-in AV shows third-party AV is installed, then it will deactivate itself and defer AV roles to the third-party AV.