I say,... GET A MAC! Honestly, a Mac is close to virus free and you wouldn't need to be bothered with getting an antivirus, which would cost more, or having to run a virus scan every other day. Why not get something that just works? Im using a mac, and it is close to perfection. Very little hanging (not too good mac...) and just works. Hassle free. However, having said that, if you need a PC for programs that are not supported on a mac, then i would advise AVG which is a free ware. Cheers!

The best 3 free anti-virus so far I think is AVG, Avast and Avira Antivir. Currently I am using Avira Antivir which is good enough and fast though got some ad/popup during updates.

A good anti-virus freeware is AVG Anti-Virus Free Edition. Alternatively you could try Avast Free Antivirus. Both have very good reviews. It's true that Mac is less targetted than PC but you should evaluate your usage patterns to see if it's a suitable option for you. Good luck :-)