I use, Avast Pro version 5 on all computers at home.
Never had a problem with it
Not bad user interface
It doesnt block ports (eg when LAN'ing)
Its always scanning in the background (I'm sure like other AV's)
Low RAM usage, from my understanding of it
Whenever i click on a file thats 'unsafe' e.g. keygens. removes it to the vault asap, and prompt's you a message of how youd like to deal with it.
been using it for over 4+ years
i'd say its better then AVG, Spyware, McCafe, Norton (old version) (prior experience with them..)