Avira Free in a heartbeat because MSE falls short, in my opinion, and when set up right, it is more effective than Avast in my experiences. Avira is also as light as a feather (or helium). Comodo firewall is apparently good, and you can tweak Avira to be extremely powerful compared to most programs that we tweak after the original default settings have been presented to us.
I have used Avast Free in the past with Online Armor and had no problems, but I have never used Comodo FW.