I use trend Pc cillan, I used to have norton but found it to be impossible to remove once it was installed, and the number of updates required used to slow my dialup to a halt. Also used McAfee, it was terrible, it buggered the registry which I had to manually correct myself, this was the direction given by McAfee technical support as there was no other way, this is a common problem with their version I had 3 years ago, I can only hope it has improved.
Trend Pc Cillan has not let me down yet, I also use spybot and adaware as well as firewalls.