Oh - and another thing: Kaspersky and NOD share the top spot (depends on which survey you look at).
But here are a few things to remember:
Kaspersky's on-access scan is good (i.e. it searches many file types), while NOD32's doesn't (not as many, but still, sizeable... Kaspersky beats here).
NOD32's heuristics scan is known industry-wide to be the best (check the internet for claims), Kaspersk'y heuristics capability isn't very good (and it's basically the heuristics that saves you before the definitions come out).
Kaspersky - it's difficult to get a working key (but I have a patch-type thing that lets you reset your 30 days trial). NOD32 has a patch that let's you use v3 for almost 40 years (till 2050)
Kaspersky can get a little bloated, but it's functionality is good. NOD32 v3 is now slicker (and definitely better than it's predecessors). Trust me, I've done ALOT of experimentation with antivirus programs
Kaspersky has an issue when it comes to false-positives (and it happened twice with me). Definition updates tend to fix it, but you never know when a safe file is regarded as a virus, and when a virus is regarded as safe.
NOD32 has failed 3 out of the 35 (or so) tests that were conducted, the lowest in the industry (I think it's Virus Bulletin that conducted the survey... can't remember.. you'll have to check it).
There you go. It's your choice now.