One thing that is really funny is that NSS Labs in a report rated TrendMicro, McAfee, and F-Secure as the three best and the ones they would recommend. I don't know who is behind NSS Labs but I totally would not touch McAfee. I think F-Secure, a Finnish AV, is pretty good. I don't know about TrendMicro.
I saw a test, I can't remember if it was AVTest or AVComparatives, where they tested AV programs against real 'zero day' malware. Norton actually had the best detection and F-Secure was in 2nd place. Kaspersky and NOD32 were pretty high. I believe very strongly, from personal experience, that Kaspersky has much better behavioral detection than Norton. And NOD32 apparently has built in HIPS protection.
MSE was not listed but according to what I found out MSE (in another test) detected only 50% of zero day malware. In comparison the average was 85% and Bitdefender scored 100%. Bitdefender has some other issues however. It slows down startup and shutdown times.
From everything I have been able to find out I still trust Kaspersky. I thought Norton was going to be really good for a while but there are reports that the 2012 Norton is buggy and it is still a mess trying to remove Norton from your computer. However, if I was sure that I could fully trust in NOD32 I would have no problem using it. It is fast, does not take up a lot of computer resources, apparently has built in HIPS protection, automatically updates, and also scans for programs that need to be updated. Version 5 looks good.
There are issues as far as I am concerned with most of the other AV programs that score well. I had a trial copy of GData and it slowed down my computer. I am not a big fan of Bitdefender either, regardless how high it scores. I have never tried Avira, except for the free version.
For me, when it comes to AV programs, for paid programs I like Kaspersky, NOD32, and maybe F-Secure.
I would like to be able to recommend MSE but for a free AV I think I would recommend Avast!.
You have to realize that it comes down to more than just detection rates, which can vary over time. Some AV programs have serious issues slowing computers down, or have slow scanning, or other problems. There is no perfect AV, but as far as I am able to determine a person would probably get good results with Kaspersky, NOD32, F-Secure, and Avast!.