When it comes to AV products, there are two things I look for:
1. How does it do against potential threats that has no virus sig in its database yet (Any product works fine against known threats, it's the new ones that are potentially most damaging and might potentially find away around your AV package).
2. How small of system resources does it take, and if it takes a lot of resources, can i turn off the crap I don't need to make it normal again?
The best place to look at this kind of data is the following independent testing site:
http://www.virusbtn.com/vb100/index
-S