AVG, Norton (Symantec), and McAfee are all far down the list when it comes to as complete coverage as you can get. There are very few anti-virus programs that do a good job. Kapersky and TrendMicro's PC-Cillin are a couple that come to mind, but I would not say they are the best. There was another one that was mentioned that I do not have any experience with (NOD 32), so I cannot comment on it, but I do intend on testing it.
The one that I've personally used for the past 4 1/2 years, and the one that our company recommends (we're a computer repair company) is Panda Anti-virus with a firewall.
We deal with virus and spyware daily. Most of the customers have either Norton, McAffe, or AVG. If those programs are doing such a great job, why do they have viruses?
In the entire time that we've been using and recommending Panda Anti-virus, we've NEVER had ANYONE call and say that they've been infected again. EVER!
Having said all that, there are no perfect programs. Panda does an amazing job protecting against virus, and it also protects against spyware as well. However, I would not trust Panda to find all the spyware.
Virus and spyware are seperate types of threats, and that means you need specific programs for each. The best anti-spyware program that I'm aware of is SpySweeper. Unfortunately, spyware can be very difficult to deal with, so we usually recommend, in addition to SpySweeper, people can use other programs such as Ad-Aware, Spybot, Spyware Doctor, CWShredder, Hijack This, and AVGs anti-spyware.