AVG is for me. Long live AVG. Hail to the master of our defense.
Oh, and did i mention it's free.
I've been using AVG since it came out to the net about 6 years ago or so. Never had to pay anything and they never asked that I do. But, as with any other shareware, you really should send them something if you plan on using it regularly.
Basically, works quietly and is a very low-resource, high quality antivirus program. Background updates that are very simple to configure to your tastes and needs.
It's a very popular antivirus program, but that's not why I choose to use it. It's just easy and works confidently. What more do you want?
Gheers,
Ron_Dogg