Like many new computers, I had Norton pre-installed with free updates for 60 days. I really didn't like how Norton disables access to an infected file and not move it to some place (Like the avast! virus chest!) for safe keeping. I had dail-up and Norton updates are a pain and takes very long to download. (It even takes long to install)
I finally got rid of it, and went to find free antivirus softwares. I found AVG at first. I tried it and it was okay. But it had no automatic update feature (AVG 6.0), and the internal updater went bad and I had to manually download updates from my computer and put it in an AVG folder. I also didn't like how the AVG resident feature works. It detects and infected file and I have to manually use the scanner to rescan the infected file and then properly remove it. Takes too much time.
I finally had enough, and went to look for a different antivirus. I did some searching and I found this site. [http://www.hackfix.org/software/antivirus.html] It had statistics about many popular antivirus softwares on trojan detection rate. AVG had a poor 64%, while Norton had 95%. I then noticed a free antivirus called avast! that was rated 98%! It was the best among the freewares. I went to avast! homepage, read stuff about it, downloaded it, and I never went back. It has everything an antivirus suppose to have, and it keeps getting better. The great support forum was also a reason I continued using avast! today!