In my opinion, Avira/Panda has been the lightest for me overall, tested on single core CPU and minimal RAM 2GB-3GB. No slowdown, or drag while using software or games, added Comodo Firewall for test and it was still quick. These two also have tested in the past for least aggressive privacy policy compared to others.
CIS was very good, but a bit heavy, and same with AVG good but a bit slow at times.
AVG and Avast have privacy policies which aquire more data and things from its user. If privacy isnt an issue then its okay.
KIS I hear can be heavy or light depends on specs I think.
I would choose Avira + Comodo. over Avast, it runs faster.