May I borrow my answer from another thread on that, my thoughts on QTS360 are still the same
My vote goes for Qihoo 360 TS, low system impact, strong cloud protection (if you wish, accompanied by Avira + BD engine for offline protection, taking more RAM), system cleaning tool (no need to use it, but implemented @ Total Security), quite often updated with new features and bug fixes. Fast reaction on new threats, polite and fast customer service. Nice and clear UI.
Please keep the difference between the Total Security version and the Total Security
Essentials version in mind: 360 TSE is "just" AV, Qihoo treats that one quite shabby, refer to the version history compared to TS. That's why I made the move to 360 Total Security.
Version History | 360 Total Security Essential
Attached is my RAM usage, next to no difference with Avira + BD activated (Cloud only is activated since yesterday, there have been some system restarts between - shutdown or Windows Update). Had a screenshot floating around here, can't find it, RAM usage all engines ~200 MB. Give me a second for a restart.
Seems to decrease with all engines enabled, but logging in felt to be a few seconds longer
See 2 comparison shots here:
Question - Best free and light antivirus?