I Would like to point out some important things regarding anti virus software.
Most 'premium' softwares check everything you download by extracting them and scanning the code for pre-defined definations.
People who would like to do nasty things to your PC are always 1 step ahead of the defination libraries anyways.
This also causes longer load times. For example everytime you play a game, load a map, models etc. the software checks them for malicious content inside of those files.
The best anti-virus out there is thinking twice before doing something. Defender and MBAM is the way to go for most people however.
Stay a safe distance from AVG, Norton, McAfee etc. bullshit. thanks.
EDIT. Also I think it's unethical for the companies mentioned above make their users think they are safe from everything if they use mentioned software.