I was recently on a virus/Trojan hunt on a friends box. We used Kaspersky and it didn't find anything. Over a lot of protestations from my friend about the poor quality of free anti virus proggys we finally ran Avira and guess what...it found/removed the two back door Trojans we were looking for. I gotta say, it may not be the best, but it finds stuff other proggies miss. Antivir scans quickly without slowing the box down too much.
I gave up on AVG when they went to automatic everything. It served me well for several years.
I find that Kaspersky is also a bit resourse intensive and slow to scan. It does the trick most of the time, as does NOD 32, for the pay to play guys.