Every other AV I tried brought my 9 year old 1.8GHz XP to a useless state. I read that ESET AV was easy on resources. It was and still is.
At first I had only NOD32 AV and used other firewall software. During those days and till this day I have never had an incident of infection or any other unwanted intrusion. In those days I must admit that I was not to bright about the dangers of the internet, and still I remained safe.
When I purchased my Win7 computer it came with a 90 trial of another security suite. After a lot of cursing Windows 7 I decided to try several of the so called free AV products. They're free if you don't count your time trying to get them to work or figure out why you can't connect or some other issues. Sometimes I think those AV's keep you safe by taking up all your time trying to get them to work.
I eventually got tired of all the trouble and re installation windows, several times, before going to ESS for both the XP and Windows 7 OS. I Haven't had one glitch with either system and only know it's there when I run a scan or see them update... Darn good software.
The only exception to my experience that I am disappointed with is the creation of the emergency CD. Never have been able to get one made correctly and my posts on the subject went without resolution.