Avast with avg antispyware 7.5.whatever_free_version_it_is_on_filehippo are a pretty unbeatable combination. User error aside they catch everything. People have been reporting avg8 is bloatware and buggy. I had to remove it from a machine last week where it was taking up 80% of the system resources. It was also trying constantly to update from non existent files.. Mileage varies, but it looks like avg8 is for the fista generation with gigs and gigs of spare ram sitting pointlessly waiting for more bloatware to fill it up with yet more junk.
I just tried out avast (never used it before), seemed ok, though my slowest non-Linux boxes are mostly Core 2 Duo's and AVG8 works ok (so far for me) so i'll stick with that. AVG spyware 7.5 wouldn't update for me so got rid and updated my spybot, ccleaner & ad-aware proggies. This thread gave me an excuse to get ALL machines up to date, (which means replacing McAfee which i've used with 100% results for years now) it'll take me a little while to get everything sorted
Admittedly, AVG 8 is certainly larger and does gobble up the memory from time to time. So far, it has been stable on both my main machines. I've been pretty happy with it so far, though i prefer 7. Otherwise i use pretty much the same set up Creaky listed, with the exception of McAfee. I've had pretty good results with all those programs.