As a whole package I would recommend COMODO Internet Security(CIS) get it here
http://forums.comodo.com/
And if you still not convinced with the AV of it then install Avira AV too to go with it.
CIS is really light on the PC
. And it's GREAT!
Avira is too a great Anti virus and is not heavy on the system as well.
If you have to pick only one then I'd recommend CIS over Avira for sure