I have used Avast for several months now & find it very easy to use. It updates itself automatically regularly. I find the user interface simple and effective. No problems with viruses since I started using it.
Don't even get me started on Norton.
Dumped them earlier this year when I could not continue with my subscription to Internet Security 2002 after a reformat. Because their website did not support a transfer for 2002 & it would have cost me £18 to phone them. My subscription had 8 months left.
If you already have Norton AV & decide to uninstall it you will need to visit their site for a small download to uninstall it completely.