I am still an Avast! fan. AVG is a good anti-virus, however it is bloated and suffers from some detection issues. It is also hated by a lot of people because of it blocks legitimate files sometimes. It does have a much better behaviour component from Avast!, however it is not implemented correctly, and some of the components in AVG conflict with each other.
Avast! also has a much slicker interface. It is easy for new people to understand and is an install and go. It also has auto-sandbox, a function that is becoming a requirement for AV's. Also, it should not contain adverts. Adverts are what ruined Avira. Avast!'s advertisements are only one screen of the UI, and is built into the interface and is non-intrusive.
If AVG can work on these flaws, then they have a full product that I may consider, but personally I consider none of the products here, however I prefer avast! if I have to.
OFF-TOPIC:
COMODO is the best free anti-virus hands-down. It contains all the pluses of these two products, and has a proper firewall, and good detection, but the icing on the cake is the AMAZING Defense+. It works very well and gives the user the option, but suggests the recommended option.