Here's one reason!You can't always tell which is the best anti-virus for your machine, as all the vendors will claim they deliver top-notch solutions, that they are leaders on the market and all that. Also, you often get facts stating that in some test a certain anti-virus ranked first, but they rarely state what competition they had. In any case, in view of recent events, Kaspersky beats the crap out of NOD32; and I will give you some facts and explain why it is so.
A computer with NOD32 and Windows XP SP2 had been infected by several Trojans. The AV found two of them and no matter how many times you would delete them, they would still pop up after rebooting. NOD32 could not disinfect the files, it just deleted them. That was pretty nasty. Couldn't get rid of the threats! Cmd didn't help much either - I guess they were stuck in the Recycler or something. Now, what I advised the owner of the affected machine was to run other AV solutions however, none of the free ones seemed to do better than NOD32, fact which was to be expected. Then she asked me what else could she buy, so I advised her to get Kaspersky Internet Security 7.0. The minute it had been installed it asked for an update and a full system scan. It took Kaspersky about 2 hours to scan a 70% full 160GB hard drive, but it found 8 threats and eliminated them all. I then rebooted the machine and scanned the folders where the viruses had been discovered - now it was all clean. So, based on this experience, I would definitely go with Kaspersky, rather than NOD32.
To us users, it's these things that count. It doesn't matter what tests and magazines say - when you're facing a threat and your AV doesn't help you enough, then you deem it useless. Users don't care what other threats it may destroy - they want to get rid of the ones THEY'RE facing! Furthermore, after this happening, I definitely became a Kaspersky fan. I, for one, don't care how much resource it will eat up - at least I will stay protected. What's the use of having security software that will not "stress" your machine, if it's also ineffective against viruses?