I can say with Avast, I've not had a major infection that I'm aware of on my system, and one of my specialties is virus/spyware removal. Also, my pc is used for gaming, so I will generally know quickly if something is up(due to slowdowns, etc.) There are genuinely some products better than others, no doubt. However, if you read the blogs I believe the CEO at Avast used to be higher up at Symantec. In the end, a lot of things boil down to a user.
Security Suites, ah, they are ok. Windows has it's own firewall built in.
For Avast, it's real time shields running on my system are these.
1. File System(real time scanning)
2. Mail
3. Web
4. P2P
5. IM
6. Network
7. Script
8. Behavior
They also have their auto sandbox, as well as webrep to scan links online. As well as the boot time scan, which I don't see Symantec having. For a free product, sounds like they compete pretty well.
Again, Windows firewall is built in, so that solves that issue. If a firewall is a big deal to you, download zone alarm or commodo, then you have complete control over what goes in and out.
Also, keep in mind, companies like Avast or AVG are going to give you decent free products because they hope that you will upgrade to the professional versions.
I guess really, for home users I do not see a great benefit of paying for antivirus any longer, unless someone is a home user who needs tech support. But if you use a decent product such as Avast, AVG, etc, and are sensible, and especially combine it with a firewall such as Zone Alarm or Commodo, if you look at things, I would say you are getting comparable protection to other paid products, perhaps better.