Free... heh. You get what you pay for. The reason that AVG is portrayed as being so good is that it doesn't detect much, so people think "Wow, this AV is really good, I am not being infected".
If you value your computer, and you purchase stuff over the internet, then pay for something good. I recommend a combination of an anti-virus and an anti-spyware/malware. They sound like the same thing, but they aren't at all. I use Kaspersky, and have for 2 years. Before that, I used ESET Nod32. They are both top-notch programs. Coupled with MalwareBytes Anti-Spyware, and you are pretty much good to go.
The best anti-virus and anti-spyware is yourself. If you are getting .exe emails, don't run them. If you download movies or songs via a program like Limewire or similar, or you are using "Cracked" versions of programs, then I can almost guarantee that there's something malicious binded with them.
If you value your personal information, then you have to be extremely vigilant in what you run, what sites you visit, who you accept any files from.
I also recommend a full format every 3 or so months. It removes everything, and keeps your system running at a good speed.