Depends how much security you need, PC-Cillin has a good set of virus patterns but the interface is crappy.
All the other mentioned AV solutions I wouldn't use by choice though if you must go Free the AVG is ok.
If you want reasonable protection go for Kaspersky or Nod32, symantec corp isn't that bad but I can't bring myself to use anthing even remotly related to Norton which is a heap of evil junk.
if you dont go to dodgy sites or use p2p or anything like that than you'll probably be fine with AVG provided you use a good firewall.