well as Capricorn says, Norton is the best right now. It is releasing the version 2003 this year or the early 2003. I actually had trouble with McAfee VirusScan 6.00 installed in Windows XP. They've got version 6.02 now -- don't know how is it -- but NAV2002 is far better in compatibility over any other anti virus program and you can't feel you have installed an anti-virus program for that uses so less resourses even in Pentium 133, 48MB RAM computer.
But I currently having problems with sending emails, incoming emails are alright. But I cannot send emails sometime. I dunno whether it has something to do woth NAV2002 as it handles out going mails. I disabled it but it still gives the trouble. I am not actually sure if it is NAV2002 to blame, but it says it has got some performance problems with Outlook 2000/XP. I am using Outlook XP and may be that. But however I still believe NAV2002 is the best and hope it will be better in NAV2003.
On the other hand McAfee has got connections with Microsoft (Hotmail emails are scanned using McAfee) so I doubt compatibility-wise McAfee should be better than NAV. We will see what is going on from the future versions of both NAV and McAfee.
I ain't sure enough to give a exact answer to say which is better, but have a current understanding that NAV performs better