The BEST FACTOR regarding an antivirus depends on what you do with your PC. For example if your antivirus consumes more RAM when scanning as well as idle/at the background, you cannot install it on a PC that is being used for CG work, either 2D or 3D.
You cannot render 2D or 3D graphics when Norton Antivirus is installed in the PC as it will consume more and more PC power which would otherwise be almost totally available if you use AVIRA or NODE 32.
NODE 32 is the best antivirus I recommend for 3D work, its revolutionary in the fact that it consumes almost no RAM when scanning and idle.
AVIRA is also a good alternative.
Am not using kaspersky anymore, and never will I use even an original verson of Norton, more space and more RAM it eats!
Also I use AVAST free edition as it has the BOOT TIME SCAN whenever my PC has some virus attack I cannot resolve the normal way, I would use several antivirus programs when my PC is heavily infected. Simply because diferent virus guards have different virus definitions.
So of course you cannot say a particular AV is the BEST.
As long as my system is running good, I would use NODE32 or AVIRA...cos am not a gamer or normal guy who uses PC for internet or word processing, I squeeze my PC to the fullest to extract the full power.