After many years running an IT repair business and seeing alot of home & business computers infested with single & multiple infections it became quite clear which antivirus programs worked and which ones didnt.
There are also the performance factors. For many years Norton (Symantec) was considered to be the best. Although it did a good job of protecting your system it was a performance slug having a huge ram footprint.
In most cases you get what you pay for. In the case of free solutions like avg, avast etc you pay nothing and thats about the amount of protection you get - nothing. But dont get me wrong its better than nothing at all.
I have been a user and reseller of NOD32 for many years and it has never let me down.
It has a low ram footprint so it wont effect peformance, picks up and cleans up many of the viruses that others miss and its reasonably priced. Best of all unlike most antivirus which wait until the virus is on your system, Nod32 can detect the virus in the TCP/IP packets before it gets onto your system and offers the ability to terminate the connection. In some cases it can clean the infection from inside a zip or rar file and still let you get the file/s you wanted. Great for thoese legitimate no cd patches your after.
In our workshop we use nod32 to scan all our customers computers data before we work on their machines or connect them up to the internet.
Nod32 has never let me down or my customers who use it with a 99% resubscription rate.
Other programs we use include: Spybot search & destroy, spyware doctor, stinger, windows defender, malwarebytes and Hijack this
To kill alot of viruses we also use Windows PE & Linux O/S to delete repropogating files.