Please don't use Bitdefender earlier versions. Bitdefender earlier version is full of bugs. Better wait for 2012 version (currently in beta) or use something with Bitdefender engine like F-secure or G-Data. They use Bitdefender engine but bug free unlike Bitdefender.

Kaspersky 2012 have been improve. Quite light already. Me? I still use avast. Avast is light and detect lots of thingss and is free.