I always liked anti viruses that left you alone and ran in the background. Avast was a good anti virus program for me, but it always had it's stupid popups at the taskbar saying something. It would even show up when I was watching a movie in full screen. Haven't used it in awhile, so I'm not sure if they changed that. Microsoft Security Essentials works fine for me. Completely in the background. Not a resource hog at all, and it updates enough to keep up with stuff I'd think. I use it on 4 computers. Malwarebytes is a good program though.
If the choice is Norton's or Nod32, then I'll say Nod32-- it's been highly rated for years and Norton's is a notorious resource hog.
With that said, I have a linux-based firewall appliance with CLAM AV running backed by Dan's Guardian content-filtering, so no AV running on any of my machines (note that this does not protect me from malware introduced by sneakernet, but my kids should know better).
On top of that, I run Ubuntu 10.4 (AMD-64), which is not a big target for malware at the moment.
Well I use Microsoft Security Essential to remove malware from my PC...
It is a pretty good anti-virus tool...Its a free application by Microsoft...
However, I used kaspersky, and it is also a very powerful anti virus software.,..
I recommend that users avoid anything that says Norton/Symantec like the plague. If a resource-heavy AV slows a computer down worse than the crap it's supposed to protect against, then what is the point?