I use the free versions of AVG and Avast both do the job very well but i would give AVG just the edge and i mean just by the smallest margin.
I have never gotton on well with AVG, always problems with it! Better to stick with the so reliable NOD32.
Its not free, however I keep using the free 30 day trial it offers over and over. It seems to work ok that way.
I think F-secure is a very good paid anti virus. They have a short free trail version. When Microsoft has a problem they turn to them. That must tell you something. They have won numerous awards. Microsoft security suite essentials are free.
I use microsoft security essentials now for 10 days and must say that im impressed. Fast and secure...for now
Nod32 antivirus is in my opinion still a fair solution for both company and individual needs. My university uses it and I use it at home - never gave me any problems. At the same time it offers frequent updates and the detection rate is far beyond average - which as far as I am concerned is great!