I've been quite happy with MSE and it's free and is updated via Windows Update so there is one less notification setting that needs to be changed. As far as CPU usage and memory footprint, all the major packages are pretty inconsequential. If your system is limited and 5% CPU usage or a few dozen megabytes are an issue for you when gaming, upgrade your system, reduce your visual settings, or run without live AV during your gaming sessions. Before I got this i7 laptop, I did all my browsing within a virtual machine running Ubuntu and ran without any AV software. Seven years of that on my old Pentium M laptop and not a single infection.