For me a "good" antivirus is one with a lot of options.
I don't like MSE as the only option you have is the time of the scheduled update, and whether you want to submit private information (to statistics only?) to Microsoft or not.
I currently have NOD32, and I'm happy with it and its options.
I regret one thing, there's no "scan everything, prompt at the end" like Kaspersky has.
When it find something, you need to answer what you want to do in order to continue the scan process, while Kaspersky show you a list of found problem only at the end.
I like to have a software Firewall for outgoing connexions.
Windows or hardware Firewall/routers only block incoming connexions if not from your set ports, but software firewall also ask you if you want to allow outgoing connexion and detects hijacking of connexion through another programs which try to contact remote servers.
I like to know who is communication.
Unfortunately, since I have NOD32, all new connexions pass through the antivirus, and the firewall only see the antivirus as connected to internet, which for me is a flaw :/
There's no option to "not automatically use nod32 HTTP protection" for newly detected programs.
I'm using Peerguardian mainly to protect my LAN, adding a security by blocking unwanted IP.