Years ago I monitored web sites on which anti virus programs were the best and it always changed back and forth of a few top brands. I have used KIS, Symantec Norton, Webroot with Spysweeper, Trend Micro, Zone Alarm and probably some I can't remember. They all were store bought. Things they had in common.
1. They all kept my computer safe
2. They all had a few false positives
3. They all cost money
4. They all wanted to control the computer causing me to constantly make adjustments (tinker)
5. They all worked fairly well with XP-Pro if you didn't mind tinkering all the time to do normal computer things.
6. All of them didn't want to work well with Windows 7 for what ever reason. These problems might of been fixed by now. Reading through many post here I don't think so.
The last straw was Trend Micro (Bought from Best Buy)I had on two computers.
Remove Trend Micro form both computers after a month of fighting with it and destroyed the CD. Then I installed MSE along with MAM and haven't looked back.
In my opinion the people that do the testing of such programs will never let a Microsoft security program ever look good whether it is or not. These testing organizations are in bed with companies who offer paid for versions.