I take your point but I alredy use the two you mention. However I experimented with a recommendation from another thread on PCA and the recommnded utilty found a nasty on my computer too. It had hidden itself as an .exe file in a legitimate proram folder.
Since switchiing to broadband in early April, I have run regular S and D, Ad-aware and AVG (now Avast) scans and have had just one nasty, discovered by Ad-Aware at the time - the reason I got it was entirely my own fault.
Anyone who has downloaded nVidia drivers from its website will probably guess why...:-)
I recently switched from AVG to Avast. My reason was that after going to the Norton site and doing an online scan it found a couple fo virus that AVG hadn't caught.
On loading Avast it found them with no trouble. Ia slo find it's reporting, updating and monitorinf to be better than AVG.
As previous posters have stated you really need to also run malware/spyware tools in conjunction with anti-virus. I use the beta verion of Microsoft Anti-spyware - it's nice as it monitors the system real-time - and then I use Spybot, A2 and Adaware just to hunt out anything else.
I intend to reduce the number of programs I use once I am confident I have found one or two that find everything (or as much as is reasonably possible).