Morris Minor Owners Club

Recent versions of Kaspersky are about as good as AV software gets although tests are very subjective.

Imho I'd either get Kaspersky (if its free anyway) or Avast.
Both being better than the free edition of AVG.

For security I use Spybot S&D for spyware protection, Avast for anti-virus and CCLeaner for housekeeping (cookies, temp files etc).
I also have 'HiJack This' to hand which is a little more specialised but handy if things do go awry with Internet Explorer.

The ones I've marked in bold I would class as essentials in a Windows environment.

I used to have the free AVG and then upgraded to the paid for version which after a while started to slow things up along with other bits and pieces, I then found out a couple of pals on cable also suffered from similar problems so I changed over to Eset Nod 32 and that has been excellent with no holdups as it really does work in the background, I now have the full package.
https://secure.eset.co.uk/forms/trial.asp