My pick for the best free AVs I tend to recommend (the order does not matter, it is simply the matter of what you want, no ADs of course):
FortiClient (install and forget, super light)
Kaspersky (signatures + cloud, a bit heavy)
Tencent PC Manager (Bitdefender signatures and more customizable than BD Free)
Panda (light and very effective in detection, but keep in mind, that it is cloud only and it does not update automatically)