I guess the best results are the one from my own experience. So far, I've tested almost all popular products since 2001 like Norton, Panda, BitDefender, Nod32, Kaspersky etc...
I've seen many machines infected with all kinds of trojans, viruses and so on. From all of them I liked only one antivirus - Kaspersky Antivirus, it is using small RAM resources and it's very effective. I saw on this page some "tests" :

AVK 2008 (1,022,418 – 99.8% AntiVir (1,020,627 – 99.6%); Avast! (1,018,204 – 99.4%); Trend Micro (1,009,662 – 98.6%); Symantec (1,006,849 – 98.3%); AVG (1,005,006 – 98.1%); BitDefender (1,003,902 – 98.0%); Kaspersky (1,003,470 – 98.0%);
Sophos (1,001,655 – 97.8%) and F-Secure (999,806 – 97.6%).

It's amusing to see such results I guess somebody is paying a lot of money for such results. And it's sad that people pays more money for a product that is ten times weaker than another one that is cheaper. For those who didn't try Kaspersky Antivirus, you can download it from here, just make sure to update it.

http://www.downloadbestsoft.com/Kasp...Antivirus.html