I know, my experience says that Webroot, Eset and somewhat Avast are the lightest AV's, people (all of them) who were using BD, KIS, AVG and later come to ESET, by my recommendation, said, If I may quote : "I CAN BREATHE NOW".
I know these tests are combining power consumption, ram usage, processor usage, but objective opinion of human observation cannot be measured by any machine, IMHO.