Please define "lightest", do you mean how it will run on your system or how much RAM and CPU cycles it uses?
Because it is not the same. System response time is how I judge lightness, some products will have low RAM and CPU usage and still makes you system run slow as a turtle. Other products may use a lot of RAM and CPU cycles and doesn't hardly effect your system's response time.
Unless you are still using Windows XP or have less than 1GB of RAM and a single core processor, RAM and CPU might have very little to do with system response time.
I really don't understand the point of these "lightest" security product threads since they never come to any resolutions.
All products will run differently on each system, unless everyone here has the exact same system with same components, you can not come to any logical conclusions.
Thanks.