Which is the best antivirus? Well IMO definitely NOT Norton! Anything but Norton.
The day after I finally decided to delete Norton Antivirus, I swear the sun shone brighter and the birds sang sweeter!
What a difference, with that dreadful program no longer hijacking the CPU for up to 60 minutes per day (up to 98% CPU for all that time) to run some mysterious, absolutely unstoppable process called ccSvcHst.exe. The (very helpful) Norton techs couldn't fix it remotely or suggest a solution, and neither can anyone else (having googled extensively and found it is a known problem for some users that goes back several years).
To be fair, obviously millions of people use Norton without experiencing this problem. But it does exist, it causes serious problems for some users, and Norton have not bothered to fix it even after several years. Why take the risk?
I replaced Norton with AVG 9 (paid for), which - touch wood - seems to work fine, and it took over from Norton without any problems, which must be a minor miracle in itself.