At some point you'll find that there is NOTHING actually FREE. There is always a catch, trust me. I have used Norton and have never had any problems. I do know people that have used the free or cheap versions and they have had problems ranging from minor to having to buy a new computer. Good luck to you.
99% of all issues people encounter with viruses, spam, pernicious toolbars, malware, etc.. are 100% avoidable if you'll just adopt a more defensive on-line attitude. I l use computers daily: Mac, PC, Linux and in the 30 years or so I've been on-line-going all the way back to the BBS days- I've had a virus problem exactly once- and that was when I lent my laptop to someone else.
Stay away from bit torrent sites (you should not be stealing music and movies anyway), never open email attachments that are from an untrusted source, NEVER EVER, EVER install a 3rd party tool bar in your browser (and make sure you don't just click OK when instailing stuff- they are out to trick you into loading their crap on your system voluntarily)- etc.. I know this may take what you consider the 'fun' out of the net- but consider that the hackers and the Anti-virus SW vendors are both working very hard to exploit your on-line laziness to their benefit
Virus protection is like a condom- it's a poor substitute for trust..
You are the best anti-virus defense. Most people get viruses because they are downloading stuff they are not supposed to anyway or are browsing controversial websites. But just in case, I use Avast. Since I don't do anything illegal on the internet it is extremely rare that I would get a virus.