I used Trend Micro which was great but they screwed it up with Live Update feature.
I have had no problem with Norton. For the last 3 years now.
McAfee is a system HOG.
There are just some people who have problems with software. A buddy lost his USB printer according to Windows it was the USB on the Motherboard. He turned it off back on then plugged in the printer and it works.
If the Anti virus is free it is not that good. My Norton updates all the time. It is quick and easy with Broadband.
But as I say whatever works for ya use it. Everyone has favs and biases to a product. Some people never have problems some do. It all depends on who built the PC in the first place. I build my own. Have since 1986 and the old 8088 12 mhz 640 meg ram , DOS days.