This has always been a big issue for me, since working in tech support requires my information and recommendations to be accurate.
Personally i find the best all-round AV to be Symantec Corporate Edition 8 or higher. That's due to the fact it requires almost zero user input and still has the 2nd highest detection rate in the industry.
If symantec isn't your scene or you don't mind the extra user-input, then Kaspersky AV is statistically proven better.
Fair enough, you shouldn't get a crippling virus with any one of the top 10 AV's, but here's a few links to show the differences in performance;
http://av-comparatives.org/images/stories/test/ondret/avc_report21.pdf
This is a test-based comparison, broken down into categorys such as worms, trojans, generic windows virii and etc.
AntiVirus Software Review 2009 - TopTenREVIEWS
This is more of a feature comparison. Note nod32 lacks protection in a few areas which can be of vital importance to the average, non-savvy computer user such as p2p downloads, email clients and lacks registry protection.
Obviously users such as the majority of the visitors here don't need such features, yet the hard facts show the best of the best to be kaspersky in #1 with symantec corp as #2 due to features and detectibility success rate.
What made me choose Kaspersky for my W7 RC install, was the fact they're offering free beta testing (Hooray

)
You can grab it at
www.kaspersky.com/windows7