No antivirus is perfect. No single product can detect all infections with malware.
I use Trend Micro's Internet Security (PC-cillin) and AFAIK, I have never had an infection as long as I keep updating it regularly. But that does not mean that it is perfect either. It is always possible that I may get infected with some malware that it does not recognise. It's the same with all anti-malwares.
NO anti-virus is capable of detecting all the signatures of viruses, but the two anti-virus which "I" like is NOD 32 and Kaspersky 2009, both are extremely good but u have to be careful what you open before fully believing anti-viruses for hassle-free computer experience
i recommend to you avast free AV. i was using AVG free all these days and i kept getting warnings about the worm "autoit.hl" even tho i had chosen the heal option before. then i tried avast which did a boot time scan and deleted that worm.