Why would you want to run two or more Anti-Virus programs? I can see a firewall and AV, and perhaps other utilities depending on the software you get, but two anti-viurs programs is generally looking for trouble at worst and waste of CPU at best.
Not all anti virus programs play nice. Of course anyone up to date on the best freeware knows right now Avast and MSE(Microsoft Security Essentials). are your best bets and they are both free. And I can tell you as a matter of fact. They play nice together. MSE is a bigger recourse hog if you run it on older PCS. But any PC made in the last 2-3 years shouldn't notice. For Malware everyone should be using Malwarebytes.
If your prudent PC nerd. Avast with Malwarebytes for good protection and performance. If you only want to run 1 and be secure. I'd say MSE since it also checks for malware.
For true security. Don't go places or download torrents that aren't highly reputable. If your constantly finding stuff. Your being very naughty for sure and mentally ********. Also keep your PC up to day.
Personally I hate AVG. If might be a good program but it does not play nice it was a resource hog and is a ***** to reinstall. Norton is terrible. More dangerous than most viruses cause of the false sense of security.
That is MHO on Anti Virus as a user of many years with fair experience with others PCs and experimenting with my own mixing and matching programs.