I have used
Bitdefender IS (latest version)
Bitdefender TS (2008)
Kaspersky IS 2012
Kaspersky IS 2011
NOD32
Norton IS 2011
Norton IS 2012
AVG Antispyware, Free ( that was in 2006 :lol: )
Threatfire
Comodo
According to my experience, BD (Bitdefender) is quite heavy on the RAM. On the other...