First off: Real World Protection Test Overview
If it is not on the above list, I do not consider it. Period.
From my personal use and installing free AV's for my clients for the past 12+ years:
I liked and recommended Avast Free for several years. It's still a great product, I take nothing away from it. In fact I still use the paid server version on several boxes I admin. Very lightweight for the comprehensive protection it provides. But I got tired of their free version tricks, subliminal, overt, and otherwise - to get people to sign up for the paid version. Too many of my clients, especially the elderly or those with little tech familiarity, fell for the tricks and paid for something they did not need.
I have also used Bit Defender Free and recommended/installed it for clients, fairly extensively. Again, an excellent product. Some few clients have complained about slower games, but I game (to much!) and I never noticed it.
I currently recommend and install Avira Free for most of my clients. It is excellent protection, (see chart linked above) very lightweight, and instead of all the tricks with registration and such, you get a straightforward, pop-up/attempt to sell you - once a day. Compared to several others, this is refreshingly direct and honest.