AV-Comparitives have recently published two reports: “On-demand Detection of Malicious Software” and “Whole product Dynamic Real World Protection Test”.
The March 2012 detection report shows that the three systems finding the most malicious software in order of success are: GData, Avira, and Kaspersky.
It also shows that those three in order of least false positives generated were: Kaspersky, GData, and Avira.
The whole product report for March 2012 shows the top three systems as: Bitdefender, GData, and Kaspersky.
Naturally the relative effectiveness of systems varies over time, but effectiveness is built on effort, not luck. Obviously more weight should be given to the most recent results, but consistent good results are also important.
I have used GData and Kaspersky so far in 2012 and can recommend them both. GData has the heaviest resource usage, but then according to the tests it makes good use of that to find the most malicious software. Kaspersky has a very nice user interface that works well for those interested in looking deeper at their system but is fairly unobtrusive for those that aren’t so interested.