I used Norton for 2 years simply because it was free. But it is the worst piece of software I have ever used. Be careful when uninstalling it Lucid Seeker, it can break your PC (Symantec has practically made it Malware) if you don't do things "properly", since the unistall is broken and it leaves broken services, files and data on your PC. Sony Ericsson's phone software is now broken because of Norton's dirty uninstall.

Symantec are bastards.

As for antivirus, I've used AVG. But I currently use Avast! which seems very good. It tells you what it is doing and what it is scanning in the background, so you know it's working. Plus, it's just easy.

And it's free.