Bitdefender free , is the one i install on family pcs because it doesnt need attention. No ads. Low memory. Perfect detection rate.
Now i would like to add virus/trojans mainly comes from your clicking habits from the net. Get a nice adblocker (ublock origin) then use common sense when browsing. Suspicious sites? Put on advanced mode on ublock origin and start blocking scripts (1st, 3rd party, blacklist 3rd party ads sites).
You could browse the web without AV and a strict ublock origin. It wouldnt be so pleasant though.
And those who say "i never get a virus" dont know about it until its too late (bank account scimmed). Be proactive, not reactive.