The main issue is the Virus Sampling.
Virus GR (http://www.virus.gr/english/fullxml/default.asp) sampling method is a file detected by any one of the antivirus software then it will be put into the sample list.
This is a big problem, as some antivirus software will getting false positive, that will make the virus sample max with virus and normal files.
The software getting most false positive will be the one getting 100% scan in virus GR, not the most accurate antivirus software.
Do not think that false positive is a price of cake! It may result antivirus software remove some program files and crash some application and even crash your system that may not able to boot!!!
ESET NOD32 till 2005, Oct getting 34th VB 100% Awards from Virus Bulletin (http://www.virusbtn.com), while the virus sample is getting from Wild List Organization (http://www.wildlist.org), it is realistic and reliable.
For detail, please visit the following links:
http://www.nod32.com.hk/support/avtesting.htm
http://www.nod32.com.hk/avtesting/response_virus_gr.htm
http://www.virusbtn.com
http://www.wildlist.org/